Use of Reclaimed Water and Sludge in Food Crop Production

Use of Reclaimed Water and Sludgein Food Crop Production

Committee on the Use of Treated Municipal Wastewater Effluents and Sludge in the Productionof Crops for Human Consumption

Water Science and Technology BoardCommission on Geosciences, Environment, and Resources

National Research Council

NATIONAL ACADEMY PRESSWashington, D.C. 1996

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Copyright © National Academy of Sciences. All rights reserved.

Use of Reclaimed Water and Sludge in Food Crop Production http://www.nap.edu/catalog/5175.html

http://www.nap.edu/catalog/5175.html

NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose mem-bers are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consistingof members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.Support for this project was provided by the U.S. Environmental Protection Agency Grant No. CX820717-01-0, U.S. Bureau of ReclamationGrant No. 3-FG-81-19140, U.S. Department of Agriculture Agricultural Research Service Grant No. 59-0700-4-067, U.S. Food and DrugAdministration, National Water Research Institute, Water Environment Research Foundation, Association of Metropolitan Sewerage Agen-cies, National Food Processors Association, Eastern Municipal Water District in California, Metropolitan Water Districts of Southern Califor-nia, Bio Gro Division of Wheelabrator Water Technologies, and N-Viro International Corporation.

Library of Congress Catalog Card Number 96-67381International Standard Book Number 0-309-05479-6Additional copies of this report are available from: National Academy Press 2101 Constitution Avenue, N.W. Box 285 Washington, D.C.20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area)

B-720Copyright © 1996 by the National Academy of Sciences. All rights reserved.

Printed in the United States of America

Cover depicts a farm field with a specialized truck for injecting sludge into the soil. A wastewater treatment plant is in the background. Artby Ellen Hill-Godfrey of Kensington, Maryland.

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Committee on the Use of Treated Municipal Wastewater Effluents and Sludge in theProduction of Crops for Human Consumption

ALBERT L. PAGE, Chair, University of California, RiversideABATENI AYANABA, Del Monte Foods, Walnut Creek, CaliforniaMICHAEL S. BARAM, Boston University Law School, MassachusettsGARY W. BARRETT, University of Georgia, AthensWILLIAM G. BOGGESS, Oregon State University, CorvallisANDREW CHANG, University of California, RiversideROBERT C. COOPER, BioVir Laboratories, Inc., Benicia, CaliforniaRICHARD I. DICK, Cornell University, Ithaca, New YorkSTEPHEN P. GRAEF, Western Carolina Regional Sewer Authority, Greenville, South CarolinaTHOMAS E. LONG, Washington State Department of Health, OlympiaCATHERINE ST. HILAIRE, Hershey Foods Corporation, Hershey, PennsylvaniaJOANN SILVERSTEIN, University of Colorado, BoulderSARAH CLARK STUART, Consultant, Philadelphia, PennsylvaniaPAUL E. WAGGONER, The Connecticut Agricultural Experimental Station, New Haven

Staff

GARY KRAUSS, Study DirectorMARY BETH MORRIS, Senior Project Assistant

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Water Science and Technology Board

DAVID L. FREYBERG, Chair, Stanford University, Stanford, CaliforniaBRUCE E. RITTMANN, Vice Chair, Northwestern University, Evanston, IllinoisLINDA M. ABRIOLA, University of Michigan, Ann ArborPATRICK L. BREZONIK, University of Minnesota, St. PaulJOHN BRISCOE, The World Bank, Washington, D.C.WILLIAM M. EICHBAUM, The World Wildlife Fund, Washington, D.C.WILFORD R. GARDNER, University of California, Berkeley (retired)THOMAS M. HELLMAN, Bristol-Myers Squibb Company, New York, New YorkCAROL A. JOHNSTON, University of Minnesota, DuluthWILLIAM M. LEWIS, JR., University of Colorado, BoulderJOHN W. MORRIS,J.W. Morris Limited, Arlington, VirginiaCAROLYN H. OLSEN, Brown and Caldwell, Pleasant Hill, CaliforniaCHARLES R. O'MELIA, The Johns Hopkins University, Baltimore, MarylandREBECCA PARKIN, American Public Health Association, Washington, D.C.IGNACIO RODRIGUEZ-ITURBE, Texas A&M University, College StationFRANK W. SCHWARTZ, Ohio State University, Columbus, OhioHENRY J. VAUX, JR., University of California, Riverside

Staff

STEPHEN D. PARKER, DirectorSHEILA D. DAVID, Senior Staff OfficerCHRIS ELFRING, Senior Staff OfficerJACQUELINE MACDONALD, Senior Staff OfficerGARY D. KRAUSS, Staff OfficerETAN GUMERMAN, Research AssociateJEANNE AQUILINO, Administrative AssociateANGELA F. BRUBAKER, Senior Project AssistantANITA A. HALL, Administrative AssistantMARY BETH MORRIS, Senior Project AssistantELLEN DE GUZMAN, Project Assistant

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Commission on Geosciences, Environment, and Resources

M. GORDON WOLMAN, Chair, The Johns Hopkins University, Baltimore, MarylandPATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, PennsylvaniaJAMES P. BRUCE, Canadian Climate Program Board, Ottawa, CanadaWILLIAM L. FISHER, University of Texas, AustinJERRY F. FRANKLIN, University of Washington, SeattleGEORGE M. HORNBERGER, University of Virginia, CharlottesvilleDEBRA S. KNOPMAN, Progressive Foundation, Washington, D.C.PERRY L. MCCARTY, Stanford University, Stanford, CaliforniaJUDITH E. MCDOWELL, Woods Hole Oceanographic Institution, MassachusettsS. GEORGE PHILANDER, Princeton University, Princeton, New JerseyRAYMOND A. PRICE, Queen's University at Kingston, Ontario, CanadaTHOMAS C. SCHELLING, University of Maryland, College ParkELLEN K. SILBERGELD, University of Maryland Medical School, BaltimoreSTEVEN M. STANLEY, The Johns Hopkins University, Baltimore, MarylandVICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida

Staff

STEPHEN RATTIEN, Executive DirectorSTEPHEN D. PARKER, Associate Executive DirectorMORGAN GOPNIK, Assistant Executive DirectorGREGORY SYMMES, Reports OfficerJAMES E. MALLORY, Administrative OfficerSANDI FITZPATRICK, Administrative AssociateSUSAN SHERWIN, Project Assistant

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Acade my has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

www.national-academies.org

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Preface

In early 1993, the U.S. Environmental Protection Agency's (EPA) Office of Wastewater Compliance andEnforcement suggested to the National Research Council's Water Science and Technology Board (WSTB) that itshould consider undertaking a study of public health and public perception issues associated with the use of treatedmunicipal wastewater and sludge in the production of crops for human consumption. At the time, EPA was justfinalizing the Part 503 Sludge Rule, Standards for the Use or Disposal of Sewage Sludge, and one of the majorimplementation concerns was with the food processing industry's reluctance to accept the practice. When EPAfirst promulgated criteria for land application of municipal wastewater sludges to cropland in 1979, some foodprocessors questioned the safety of selling food crops grown on sludge-amended soils and their liability. Inresponse, the principal federal agencies involved—EPA, the U.S. Food and Drug Administration (FDA), and theU.S. Department of Agriculture (USDA)—developed a Joint Statement of Federal Policy in 1981 to assure thatcurrent high standards of food quality would not be compromised by the use of high quality sludges and propermanagement practices. Nevertheless, the food processing industry remains concerned about safety and marketacceptability, and at least one company has adopted an official policy that bans the purchase of any crops grownon fields receiving municipal sewage sludge or treated municipal wastewater. With the issuance of the Part 503Sludge Rule in 1993, public concerns with a number of technical, regulatory, and environmental issues havesurfaced. Because cropland application of both sludge and wastewater represent important management options,municipal wastewater management officials have a vital interest in the feasibility of these practices.

Therefore, in mid-1993, WSTB formed a committee representing diverse expertise and perspectives toconduct an independent study of the safety and practicality of the use of these materials for the production of cropsfor human consumption. The study sought to review (1) the historical development, rationale, and scope of thepractice of treating municipal wastewater and sludge in the United States; (2) wastewater treatment technologiesand procedures for agricultural use of these materials; (3) effects on soils, crop production, and ground water; (4)public health concerns about microbiological agents and toxic chemicals; (5) existing regulations

PREFACE vii

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and guidelines; and (6) economic, liability, and institutional issues. The committee based its review on existingpublished literature and discussions with experts in the field. The committee was not constituted to conduct anindependent risk assessment of possible health effects, but instead to review the method and procedures used byEPA in its extensive risk assessment, which was the basis for the Part 503 Sludge Rule.

The committee met five times over a 17-month period including field visits to the Irvine Ranch WaterDistrict in California, the CONSERV II Water Reclamation Program of Orange County and Orlando, Florida, andthe Disney World, Florida reuse programs. The committee also held a one-day workshop at Rutgers University inNew Brunswick, New Jersey to hear from researchers, public interest groups, farm credit bureaus, farmers, andstate and city planners on land application of municipal sludge in the Northeast.

The committee focused primarily on the issues surrounding the use of treated municipal wastewater effluentsand treated sludge in food crop production, concentrating on the uptake of chemical constituents and pathogens byfood crops. The study did not include an investigation of what happens after the crops are harvested (e.g.,processing of food products). Further, the committee was not constituted to evaluate site-specific implementationof wastewater effluent and sludge reuse projects, or to compare the relative merits and risks of various other formsof disposal or beneficial uses. However, the committee recognized that in addition to the safety and practicality ofusing these materials on food crops, there are many implementation issues involved with the agricultural use ofmunicipal wastewater and sludge including the degree to which the regulations are implemented and enforced, thepublic confidence in local reuse programs, local nuisance and traffic problems, environmental and product liabilityissues, and overall public perceptions. In several of these areas, this report notes particular findings that shouldreceive the attention of federal, state, and local authorities responsible for implementing reuse projects.

It is hoped that this report will be particularly useful to food processors, states, and municipalities in assessingthe use of treated municipal wastewater and sludge in producing crops for human consumption. It highlightspublic concerns and regulatory issues likely to be faced, and also identifies some additional areas for research.

The Committee on the Use of Treated Municipal Wastewater Effluents and Sludge in the Production of Cropsfor Human Consumption consisted of 14 members with experience in soil and crop science, agriculturalengineering, wastewater and sludge treatment, soil microbiology, toxicology, ecology, infectious disease, publichealth, economics, law, and other relevant fields. The committee gained insights from a far larger group byinviting guests to its meetings, participating in field trips, and reviewing the literature. My great appreciation goesto the committee, each of whom gave significant time and energy to create this report. Additionally, I would like tothank Rufus Chaney and Richard Bord for providing their time and resources to the study. I want to thank the staffof the WSTB, especially Gary Krauss, study director, and Mary Beth Morris, project assistant. I would also like tothank the study sponsors: the EPA, the U.S. Bureau of Reclamation, the USDA, the FDA, the National WaterResearch Institute, the Water Environment Research Foundation, the National Food Processors Association, theAssociation of Metropolitan Sewerage Agencies, California's Eastern Municipal Water District,

PREFACE viii

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the Metropolitan Water Districts of Southern California, Bio Gro Division of Wheelabrator Water Technologies,and N-Viro International Corporation. Without this support, the study would not have occurred.

Albert Page

University of California, Riverside

PREFACE ix

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PREFACE x

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Contents

EXECUTIVE SUMMARY 1 Background 1 Conclusions and Recommendations 3 Concluding Remarks 13

1 INTRODUCTION 14 Reference 16

2 MUNICIPAL WASTEWATER, SEWAGE SLUDGE, AND AGRICULTURE 17 Historical Perspectives 17 Irrigation with Reclaimed Water 24 Use of Sewage Sludge in Agriculture 34 Summary 39 References 40

3 MUNICIPAL WASTEWATER AND SLUDGE TREATMENT 45 Quantity and Quality of Municipal Wastewater Effluent and Sludge 45 Conventional Wastewater Treatment Processes 47 Treatment to Facilitate Crop Irrigation With Reclaimed Water 50 Sludge Treatment Processes 51 Industrial Wastewater Pretreatment 56 Summary 60 References 60

CONTENTS xi

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4 SOIL, CROP, AND GROUND WATER EFFECTS 63 Sludge as a Source of Plant Nutrients 63 Treated Municipal Wastewater as a Source of Plant Nutrients and Irrigation Water 66 Effects of Sludge and Wastewater on Soil Physical Properties 67 Effects of Sludge and Wastewater on Soil Chemical Properties 69 Effects of Sludge on Soil Microorganisms 76 Effects on Ground Water 78 Landscape-Level Considerations 81 Summary 82 References 83

5 PUBLIC HEALTH CONCERNS ABOUT INFECTIOUS DISEASE AGENTS 89 Infectious Disease Transmission 89 Infectious Disease Risk 92 Monitoring Infectious Disease Potential 93 Public Health Experience With the Use of Reclaimed Water and Sludge 95 Summary 96 References 97

6 PUBLIC HEALTH CONCERNS ABOUT CHEMICAL CONSTITUENTS IN TREATEDWASTEWATER AND SLUDGE

100

Fate of and Exposure to Organic Chemicals 101 Fate of and Exposure to Trace Elements in Sludge 109 Nonspecific Health Effects of Sludge and Wastewater 111 Summary 113 References 114

7 REGULATIONS GOVERNING AGRICULTURE USE OF MUNICIPAL WASTEWATER ANDSLUDGE

120

Regulatory Background 120 Federal Standards for the Control of Pathogens in Sewage Sludge 122 Approaches to Toxic Chemical Regulation in Sludge and Wastewater Land Application 125 Development of U.S. Chemical Pollutant Standards for Agricultural Use of Sewage Sludge 127 Evaluation of Federal Standards for Chemical Pollutants in Sewage Sludge 134 Regulations and Guidance for Agricultural Use of Municipal Wastewater, 139 Summary 147 References 149

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8 ECONOMIC, LEGAL, AND INSTITUTIONAL ISSUES 151 Economic Incentives for Land Application of Treated Municipal Wastewater and Sludge 151 Managing Residual Risks 158 Other, Related Government Regulations 164 Summary 171 References 172

APPENDIX 175 Committee Member Biographical Information 175

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CONTENTS xiv

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Executive Summary

BACKGROUND

The use of treated municipal wastewater effluent for irrigated agriculture offers an opportunity to conservewater resources. Water reclamation can also provide an alternative to disposal in areas where surface waters have alimited capacity to assimilate the contaminants, such as the nitrogen and phosphorus, that remain in most treatedwastewater effluent discharges. The sludge that results from municipal wastewater treatment processes containsorganic matter and nutrients that, when properly treated and applied to farmland, can improve the physicalproperties and agricultural productivity of soils, and its agricultural use provides an alternative to disposal options,such as incineration, or landfilling.

Land application of municipal wastewater and sludge has been practiced for its beneficial effects and fordisposal purposes since the advent of modern wastewater management about 150 years ago. Not surprisingly,public response to the practice has been mixed. Raw municipal wastewater contains human pathogens and toxicchemicals. With continuing advances in wastewater treatment technology and increasingly stringent wastewaterdischarge requirements, most treated wastewater effluents produced by public treatment authorities in the UnitedStates are now of consistent, high quality. When treated to acceptable levels or by appropriate processes to meetstate reuse requirements, the effluent is referred to as ''reclaimed water." Sewage sludge can also be treated tolevels that allow it to be reused. With the increased interest in reclaimed water and the promotion of agriculturaluse for treated sludge, there has been increased public scrutiny of the potential health and environmentalconsequences of these reuse practices. Farmers and the food industry have expressed their concerns that suchpractices—especially the agricultural use of sludge—may affect the safety of food products and the sustainabilityof agricultural land, and may carry potential economic and liability risks.

Reclaimed water in the United States contributes a very small amount (probably much less than one percent)of water to agricultural irrigation, mainly because the extent of the practice is limited both by regional demandsand the proximity of suitable agricultural land to many municipal wastewater treatment plants. Most reclaimedwater goes towards various nonpotable urban uses such as irrigating public landscapes (parks, highway medians,lawns, etc.), air-conditioning and cooling, industrial processing, toilet-flushing, vehicle-washing, and

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construction. Irrigation of residential lawns and/or gardens with reclaimed water is becoming increasingly popularwhere dual plumbing systems to facilitate water reuse have been installed; however, this report concentrates onagricultural uses of reclaimed water, and not residential use.

Sewage sludge (or simply, "sludge") is an inevitable end product of modern wastewater treatment. Many ofthe organic solids, toxic organic chemicals, and inorganic chemicals (trace elements) are removed from the treatedwastewater and concentrated in the sludge. An estimated 5.3 million metric tons per year dry weight of sludge arecurrently produced in the United States from publicly owned treatment plants. This amount will surely increase as alarger population is served by sewers and as higher levels of wastewater treatment are introduced.

Sludge disposal has always represented a substantial portion of the cost of wastewater management. Over thepast 20 years, restrictions have been placed on certain sludge disposal practices (e.g., ocean dumping and landfilldisposal), causing public wastewater treatment utilities to view the agricultural use of sludge as an increasinglycost-effective alternative. Currently, 36 percent of sludge is applied to the land for several beneficial purposesincluding agriculture, turfgrass production, and reclamation of surface mining areas; 38 percent is landfilled; 16percent is incinerated; and the remainder is surface disposed by other means.

The Midwest has a long history of using treated sludge on cropland. Much of the cropland that receivessludge is used to grow hay, corn, and small grains for cattle feed, and public acceptance generally has beenfavorable. In Madison, Wisconsin, for example, the demand for sludge as a soil amendment exceeds the localsupply. With ocean disposal of sludge no longer allowed, New York City and Boston—among other coastal cities—ship much of their sludge to other parts of the country. A portion of the sludge produced in the Los AngelesBasin is transported to a large farm near Yuma, Arizona.

If all the municipal sludge produced in the United States were to be agriculturally applied at agronomic rates,it would only be able to satisfy the nitrogen needs of about 1.6 percent of the nation's 1,250 million hectares (309million acres) of cropland. About one quarter of this cropland is used to grow food for human consumption, ofwhich 2 percent grows produce crops that can be consumed fresh. Thus, in a national context, the amount of foodcrops produced on fields receiving sludge would remain very small. Nevertheless, the local availability ofagricultural land, combined with other regional and local concerns, is an important factor in sludge managementdecisions. While many western and midwestern states have ample agricultural land relative to the amount ofsludge produced, land is less available in other regions. In New Jersey, for example, over half the state's croplandwould be needed to receive sludge application to avoid other forms of disposal or out-of-state disposal. RhodeIsland would need essentially all of its cropland to satisfy its sludge disposal needs through in-state agriculturaluse. The level of public acceptance for agricultural use of sludge varies considerably. Nuisance (e.g. odors andtraffic), environmental, and safety issues are legitimate concerns that must be addressed by regulatory policy andmanagement programs.

In February 1993, the U.S. Environmental Protection Agency (EPA) promulgated Standards for the Use orDisposal of Sewage Sludge (Code of Federal Regulations Title 40, Parts 257, 403, and 503, and hereafter referredto as the "Part 503 Sludge Rule"). The rule builds on a number of federal and state regulations that aim to reducepollutants entering the municipal waste stream through source controls and industrial pretreatment programs thathave reduced the

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levels of contaminants in the sludge as well as in the final effluent. The Part 503 Sludge Rule defines acceptablemanagement practices and provides specific numerical limits for selected chemical pollutants and pathogensapplicable to land application of sewage sludge. In this context, sewage sludge—traditionally regarded by manygroups as an urban waste requiring careful disposal—is now viewed by the wastewater treatment industry, theregulatory agencies, and participating farmers as a beneficial soil amendment.

EPA believed that both water reclamation and sludge beneficial use programs could benefit from anindependent assessment of the public health and environmental concerns that have been raised by the foodprocessors concerning land application of treated municipal wastewater and sludge. In mid-1993, at the suggestionof EPA, and with support of a number of co-sponsors, the National Research Council (NRC) undertook this studyto examine the use of treated municipal wastewater and sludge in the production of crops for human consumption.The study reviews the current state of the practice, public health concerns, existing guidelines and regulations, andimplementation issues. The report makes a number of recommendations resulting from the study that aresummarized below.

CONCLUSIONS AND RECOMMENDATIONS

Irrigation of food crops with treated municipal wastewater has been effectively and safely practiced in theUnited States on a limited scale. The public has generally accepted the concept of wastewater irrigation as part oflarger and more comprehensive water conservation programs to reclaim wastewater for a variety of nonpotableuses. Where reclaimed water has been used for food crop production, the state standards for wastewater treatmentand reuse, along with site restrictions and generally good system reliability, have insured that food crops thusproduced do not present a greater risk to the consumer than do crops irrigated from conventional sources.

The beneficial reuse of municipal sludge has been less widely accepted. Federal regulations are designed toassure that sludge application for the production of food crops does not pose a significant risk from theconsumption of foods thus produced. However, the parties affected by these reuse programs—local communities,crop growers, food processors, and the consumer—remain concerned about the potential for exposure tocontaminants, nuisance problems, liability, and adequacy of program management and oversight. Sludgemanagement programs based on agricultural sludge use can involve many potentially responsible parties, and cancross agency, state, and federal jurisdictional boundaries. Therefore, municipalities, public utilities, crop growers,and food processors must be able to provide well-managed and reliable programs that address, and are open to,community, business, health, agronomic, and environmental concerns.

Adequacy of Existing Regulations for Pathogens in Reclaimed Water and Sludge

Municipal wastewater contains a variety of pathogenic (infectious) agents. When reclaimed water or sludge isused on fields producing food crops, the public health must be protected.

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This can be achieved by proper wastewater or sludge treatment and site management that reliably reduces thepathogens to acceptable levels.

There are no federal regulations directly governing the use of municipal wastewater to irrigate crops.However, EPA provided guidelines for reclaimed water quality and its use for crop irrigation in its 1992Guidelines for Water Reuse. There are currently 19 states that regulate the practice by setting criteria for reclaimedeffluent quality, such as microbiological limits or process standards; crop restrictions; or by waiting periods forhuman or grazing animal access or before crop harvest. State regulations vary; some require very high-qualityeffluents to reduce the concentration of pathogens to levels acceptable for human contact prior to irrigation. Othersdepend on the use of crop restrictions and site limitations, thus allowing required time for pathogens to decrease toacceptable levels. In general, modern wastewater treatment procedures incorporate monitoring and technicalredundancies that provide system reliability and protection against exposure to pathogens.

The strategy for regulating pathogens in the agricultural use of sludge is similar. The Part 503 Sludge Rulerequires the use of either Class A pathogen criteria, in which the sludge is considered to be safe for direct publiccontact, or Class B pathogen criteria, in which site and crop restrictions are required.

Class A (safe for public contact) microbial standards or process standards for sludge appear to be adequatefor public health protection. The Part 503 Sludge Rule allows for direct testing of pathogens (bacteria, viruses, andhelminths), and the use of salmonella or fecal coliform testing as alternative indicators to determine Class Asludge quality. The prescribed methods for the testing of salmonella are of questionable sensitivity. Until suchtime as more precise methods are developed and accepted, the present test for salmonella should not be used as asubstitute for the fecal coliform test; rather, it should be run in concert with that test or in situations in which thefecal coliform results are in question, such as may happen under some operating conditions. The salmonella test isless precise because of the relatively low numbers of salmonella present compared to fecal coliform.

Restrictions on the use of Class B sludge require allowing a suitable length of time for die-off of helminthova, which can be transmitted to humans via improperly cooked, contaminated meat. The control of helminthparasites is achieved largely through public health education (e.g., the need for thorough cooking of meat) andgovernment meat inspection, as well as controls over applications of wastewater and sludge to land. Based on areview of U.S. studies, the Part 503 Sludge Rule requires a 30-day waiting period before cattle can graze on Class Bsludge-amended fields. A recent investigation in Denmark indicates that the beef tapeworm (Taenia sp.), one ofthe helminth group, may survive in sludge-treated fields for up to one year. Although the evidence comes from asingle study, there is reason to believe that the length of the waiting period for grazing following sludgeapplication to pastures needs to be re-examined.

There have been no reported outbreaks of infectious disease associated with a population's exposure—eitherdirectly or through food consumption pathways—to adequately treated and properly distributed reclaimed water orsludge applied to agricultural land. Reports and available epidemiological evidence from other countries indicatethat agricultural reuse of untreated wastewater can result in infectious disease transmission. The limited number ofepidemiological studies that have been conducted in the United States on wastewater treatment

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plant workers or populations exposed to various reclaimed water or treated sludge via land application projectsindicate that exposure to these materials is not a significant risk factor. However, the value of prospectiveepidemiological studies on this topic is limited because of a number of factors, including a low illness rate—ifany—resulting from the reuse practice, insufficient sensitivity of current epidemiological techniques to detectlow-level disease transmission, population mobility, and difficulty in assessing actual levels of exposure.

Infectious diseases of the types potentially associated with municipal wastewater are under-reported andexposures are scattered, so that some effects may well go unrecorded. From a public health point of view, themajor microbiological considerations for evaluating any reuse management scheme are the ability to effectivelymonitor treatment efficacy and the reliability of the process used to reduce pathogens to acceptable levels.

Recommendations

• Until a more sensitive method for the detection of salmonella in sludge is developed, the present testshould be used for support documentation, but not be substituted for the fecal coliform test inevaluating sludge as Class A.

• EPA should continue to develop and evaluate effective ways to monitor for specific pathogens insewage sludge.

• EPA should re-evaluate the adequacy of the 30-day waiting period following the application ofClass B sludge to pastures used for grazing animals.

Adequacy of Existing Regulations for Harmful Chemicals in Reclaimed Water and TreatedMunicipal Sludge

Reclaimed Water

States that regulate the use of reclaimed water for crop irrigation have focused on its microbiological qualityand have not typically set human health criteria for harmful inorganic (trace elements) and organic chemicals inthe reclaimed water. Instead, reliance is placed on the wastewater treatment processes to reduce these constituentsto acceptable levels in reclaimed water.

Potentially harmful trace elements, such as arsenic, cadmium, cobalt, copper, lead, mercury, molybdenum,nickel, selenium, and zinc are found in treated municipal wastewater effluents. In 1973, the National Academy ofSciences issued a report on water quality criteria that recommended limits on the concentration of trace elements inirrigations water regard to their effects on crop production. These agricultural irrigation guidelines have beengenerally accepted by EPA and others. Reclaimed water that has received a minimum of secondary treatmentnormally falls within these guidelines. While wastewater treatment processes typically used in the United Statesare not usually intended to specifically remove trace elements from the

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waste stream, most of the trace elements are only sparingly soluble and tend to become concentrated in theresidual solids or sludge fraction. Chemical production and use bans, industrial pre-treatment programs, andmunicipal wastewater treatment have been effective in reducing the levels of toxic constituents in wastewatereffluents to acceptable levels.

Wastewater treatment processes also remove many toxic organic chemicals in the wastewater stream throughvolatilization and degradation. Those that remain in the final effluent may volatilize or decompose when reclaimedwater is added to soil. Consequently, only negligible quantities of toxic organic chemicals from municipalwastewater systems—those relatively resistant to decomposition—will persist in soils for an extended period. Ingeneral, toxic organic chemicals, especially those that persist in the soil, are not taken up by plants when the waterapplication rates are commensurate with crop needs. Therefore, the immediate or long-term threat from organicchemicals to humans consuming food crops irrigated with reclaimed water is negligible.

Treated Municipal Sludge

Potentially harmful chemicals (largely, trace elements and persistent organics) become concentrated in thesludge during the wastewater treatment process. Following repeated land applications, trace elements, except forboron, will accumulate in the soil to, or slightly below, the depth of sludge incorporation. The persistent organicchemicals degrade over time in soils. Degradation rates are dependent on the chemical in question and on soilproperties.

The Part 503 Sludge Rule for the agricultural use of sludge sets criteria for concentrations of 10 traceelements in sludge; arsenic, cadmium, chromium1, copper, lead, mercury, molybdenum1, nickel, selenium1, andzinc. The rule is based on a risk-assessment approach that considered the effects of these trace elements andorganic chemicals of concern on crop production, human and animal health, and environmental quality. Except forcadmium, these trace elements are not ordinarily taken up by crop plants in amounts harmful to humanconsumers. EPA regulations for cadmium in sludge are sufficiently stringent to prevent its accumulation in plantsat levels that are harmful to consumers.

In deriving pollutant loading rates for land application of sewage sludge, EPA considered 14 transportpathways and, in all cases, selected the most stringent value as the limit for each pollutant. For the 10 regulatedinorganic pollutants, the most stringent loading rates were derived from pathways that involved a child directlyingesting sludge or from pathways involving effects on crops. This resulted in significantly lower pollutant limitsthan would have been the case had they been set by human food-chain pathways involving human consumption offood crops, meat or dairy products. Therefore, when sludges are applied to land according to the Part 503 SludgeRule, there is a built-in safety factor that protects against human exposure to chemical contaminants via humanfood-chain pathways.

Available evidence indicates that most trace organic chemicals present in sludge are either not taken up or aretaken up in very low amounts by crops after sludge is applied to land. The

1Selected criteria have since been rescinded or are under review by EPA.

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wastewater treatment process removes most of these organic chemicals, and further reduction occurs when sludgeis processed and after it is added to soil. Consequently, only negligible quantities of toxic organic chemicals frommunicipal wastewater systems will persist in soils for an extended period. Recent studies suggest that plant tissuesmay absorb volatile toxic organic chemicals from the vapor phase of volatile compounds; however, the aerationthat occurs during treatment of wastewater and during many sludge treatment processes removes most of thevolatile organic chemicals at the treatment plant.

This study revealed some inconsistencies in EPA's approach to risk assessment and its technical interpretationfor development of the Part 503 Sludge Rule, although the inconsistencies do not affect food safety. To improvethe overall integrity of the regulation, EPA should address the exemption of organic pollutants and the marketingof sludge products to the public.

Exempting Organic Pollutants EPA chose not to regulate organic pollutants in the Part 503 Sludge Rulebecause all priority organic pollutants that were considered fell into at least one of the three exemption categories:(1) the pollutant has been banned in the United States and is no longer manufactured, (2) the pollutant wasdetected by EPA in less than 5 percent of the sludge from wastewater treatment plants sampled in a nationalsewage sludge survey, or (3) the concentration of the pollutant was low enough that it would not exceed the risk-based loading rates. Nevertheless, PCBs and aldrin/dieldrin occurred at higher than 5 percent detection frequency,and the concentrations of PCBs, hexachlorobenzene, benzo(a)pyrene, and N-nitrosodimethylamine would result inpollutant loadings exceeding EPA's risk-based limits in a small percentage of sludges. Some of these have beenbanned but persist in the environment. While the probability that the compounds would affect human-consumedcrops is very low, the potential for human exposure to these chemicals through other pathways as defined in thePart 503 Rule should be re-evaluated.

The basis for exempting organic chemical pollutants rests, in part, on the integrity of the 1990 NationalSewage Sludge Survey (NSSS)—the data base used by EPA to determine concentrations of pollutants in sludge.The survey has been criticized because sludge samples analyzed from the treatment plants varied in their watercontent which caused inconsistencies when deriving standardized detection limits of chemicals. As a result,estimates of frequencies and concentrations for certain organic chemicals may not be reliable. A credible data setof toxic chemical concentrations in sewage sludge based on a nationwide survey is essential. To update itsinformation on sludge quality, EPA plans to repeat the survey in the near future. In conducting a second NSSS,EPA should strive to improve the integrity of the data by using more consistent sampling and data-reportingmethods.

Recommendation

• A more comprehensive and consistent survey of municipal wastewater treatment plants is needed toshow whether or not toxic organic compounds are present in sludges at concentrations too low topose a risk to human and animal health and to the environment. In conducting a second NSSS, EPAshould strive to improve the integrity of the data by using more

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consistent sampling and data-reporting methods. The EPA should not exclude chemicals fromregulatory consideration based solely on whether or not those chemicals have been banned frommanufacture in the United States (e.g., PCBs) since they are still found in sludges from manywastewater treatment plants.

Marketing Sludge Products to the Public In addition to its use on agricultural land, sludge can be marketedand distributed to the public for home gardening and landscaping purposes. EPA has used the term "ExceptionalQuality" (EQ) to refer to sludge that meets specified low pollutant and pathogen limits and that has been treated toreduce the level of degradable compounds that attract vectors. EQ sludge is a product that required no furtherregulation. EPA allows sludge that is sold or given away to the public to exceed the EQ chemical pollutantconcentrations with the stipulation that prescribed application limits not be exceeded. However, there is littleassurance that the home gardener or landscaper will either be aware of or be able to follow these requirements, noris there a method for tracking the disposition of sludge marketed to the public. Allowing sludge with less than thehighest quality chemical pollutant limits to be used by the public opens the door to exceeding regulatory limits,and thereby undermines the intent of Part 503 and public confidence in the law.

Recommendation

• The Part 503 Sludge Rule should be amended to more fully assure that only sludge of exceptionalquality, in terms of both pathogen and chemical limits, is marketed to the general public so thatfurther regulation and management beyond the point of sale or give-away would not be necessary.

Soil, Crop, and Ground Water Effects

Reclaimed Water

Guidelines for the chemical quality of water used in agricultural irrigation have been generally accepted sincerecommended limits were set by a National Academy of Sciences report in 1973. These guidelines concernpotential toxicity to plants or to crop productivity. Where industrial pretreatment programs are effectivelyimplemented (or where industrial input is low), reclaimed water that has received a minimum of secondarytreatment will normally meet these recommended limits for irrigation water quality.

While the plant nutrients in treated effluents are generally considered a supplemental fertilizer source, theapplication rates are not easily controlled compared to commercial fertilizer operations. Wastewater irrigationcould exceed the nitrogen and phosphorus requirements of many crops during the growing season. Further, plantsrequire nutrients and water at different stages in the growth cycle and the timing of irrigation may not correspondto times when plant

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nutrients are needed. Wastewater applications at times when the plant nutrient needs are low can lead to excessivevegetative growth, can affect crop maturity, and can cause leaching of nitrate nitrogen and possible nitratecontamination of ground water.

The application of wastewater effluents to soils may pose some risk of ground water contamination byviruses and bacteria; however, that risk can be minimized by adequate disinfection of reclaimed wastewater and byslow infiltration rates.

Recommendation

• Those who irrigate crops with treated municipal wastewater should be aware of the concentrationof nutrients (nitrogen and phosphorus) in the reclaimed water and should adjust fertilizer practicesaccordingly in order to avoid undesirable vegetative growth or potential contamination of groundwater.

Treated Municipal Sludge

Municipal sewage sludge is a source of nitrogen and phosphorus in crop production. The addition of organicmatter through successive sludge applications improves the physical properties and productivity of soils. Whenused at agronomic rates for nitrogen and phosphorus, sewage sludge can usually satisfy crop requirements formany other nutrients as well, with the possible exception of potassium. EPA's Part 503 Sludge Rule specifies theannual and cumulative loadings of trace elements in sludge-amended soils, and, based on currently availableinformation, these limits are adequate to protect against phytotoxicity and to prevent the accumulation of theseelements in crops at levels harmful to consumers.

Because repeated sewage sludge applications lead to accumulations of trace elements in soil, concern hasbeen expressed over possible adverse effects associated with the use of sludge on soils that are acidic or maybecome acidic. However, as long as agricultural use of treated sludge is in keeping with current regulations andacid soils are agronomically managed, no adverse effects are anticipated. The Part 503 Sludge Rule is based onapproximately 20 years of research and experience in applying sewage sludge to cropland. While this has providedan adequate knowledge base for developing the regulations, continued monitoring of trace elements in soils overlonger time periods is desirable.

As in all farm operations, proper management is needed to avoid the buildup of nitrates. Typically, sludgescomprise approximately 1 to 6 percent organic and inorganic nitrogen on a dry weight basis. The soluble inorganicforms are immediately available to plants, but the organic forms must first be mineralized to plant-availableforms. For sludge to be efficiently used as a source of available nitrogen, the mineralization of organic nitrogenmust be taken into account to avoid overfertilization and potential leaching of excess nitrate-nitrogen into groundwater.

Most sludges supply more than enough phosphorus to satisfy crop needs when applied as a source ofnitrogen. In certain soils, available phosphorus may be excessive, particularly

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where animal manure is plentiful and where impacts to surface water quality are of concern. In these situations,soil phosphorus levels should be monitored and sludge application rates be adjusted to correspond to cropphosphorus rather than nitrogen needs.

Heavy metals are not mobile in soils, and their transport to ground water as a result of sewage sludgeapplication at agronomic rates is unlikely. Likewise, toxic organic compounds in sludge are not likely tocontaminate ground water because their concentrations are low, because they are volatilized or biodegraded insoils, or because they are strongly sorbed to soil particles. Because of predictable pathogen die-off and because ofthe immobilization of micro-organisms on sludge and soil particles, the risk of transporting viruses, bacteria, andprotozoa to ground water due to sludge application is negligible as long as sludge is properly treated and applied toor incorporated into unsaturated soils. As with all agricultural soil amendments, sludge use must be managedproperly to avoid contamination of surface or ground waters.

Recommendations

• When determining sludge and fertilizer application rates, an analysis of the rates of organicnitrogen mineralization should be performed in order to avoid buildup of excess nitrate-nitrogen.Nitrate-nitrogen that is not taken up by plants may contribute to excess fertilization and leaching.Where excess phosphorus is of concern, soil phosphorus levels should be monitored and sludgeapplication rates should be adjusted to correspond to crop phosphorus rather than nitrogen needs.

• As more croplands are treated with municipal sludges and reach their regulatory limit of chemicalpollutant loading from sludge applications, additional information will be needed to assesspotential, long-term impacts of sludge on ground water quality and on the sustainability of soils forcrop production.

Economic, Legal, and Institutional Issues

In addition to human health and environmental concerns, there are other barriers to increased acceptance oftreated municipal wastewater and/or sludge application in the production of food crops. In general, however,barriers to acceptance apply more to agricultural use of sludge than to crop irrigation with reclaimed water. Thesepotential barriers include lack of economic incentives for the farmer, lack of public confidence in the adequacy ofregulatory systems to ensure compliance, agribusiness concerns with potential liability or economic losses due todecreases in both land value and crop value, and public concerns over nuisance factors.

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Economic Considerations

There are negligible economic incentives for food processors to accept crops produced with reclaimed wateror treated sludge. Benefits in terms of lower raw food costs are likely to be minimal, potential risks could lead toliability, and the negative public perception of food crops produced using these materials could have a detrimentalimpact on consumer demand.

Even though the value of the water and nutrients represents only a small percentage of total farm productioncosts, there are many cases of clear economic incentives for society as a whole as well as for municipalwastewater treatment plants to pursue cropland reuse options. In water-scarce areas, reclaimed water should havevalue comparable to that of irrigation water from conventional sources. Where alternative irrigation water ischeaply available, there are only limited incentives for farmers to apply reclaimed water. Limited economicincentives exist for farmers to use sludge because fertilizer is relatively inexpensive and sludge use may entailadditional management concerns. It may be appropriate to pay the farmer where the regulatory compliance costsassociated with using reclaimed water or treated sludge exceed their beneficial use values. However, paymentsshould not encourage excessive application rates that would interfere with the proper agronomic use of thesematerials.

Recommendation

• Any payment program designed to promote agricultural use of treated effluents or treated sludgeshould be carefully structured to avoid the creation of incentives to apply reclaimed water or sludgeat rates in excess of agronomic rates, and to avoid undermining farm management practices neededto protect public and occupational health and the environment.

Public Perception and Liability

The public is concerned about the health and environmental risks associated with beneficial land applicationof sludge, particularly in areas where land application has only recently been implemented or considered. Some ofthis concern is not scientifically supportable, and should be addressed with education programs and early publicinvolvement in the design of land-application programs. In addition, private-sector forces can deter violations ofthe law and mismanagement by the various parties involved in reuse programs. Private-sector forces includecommon-law liability, market forces, and voluntary self-regulation such as codes of conduct, worker training andcertification, and audits. Although insurance coverage and indemnification contracts for the farmer are usefulmeans of self-regulation and protection against certain kinds of economic harm, it is unlikely that they will besufficient to satisfy all concerns of the farmer, food processors, general public, and the affected community. Thus,public concerns about real or perceived residual risks create business risks and militate against agricultural use ofsludge and reclaimed water despite the federal or state regulatory safeguards. Proponents of cropland


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application of sludge and wastewater must, therefore, address such public concerns if they are to achieve theirgoals.

Recommendations

• States and municipalities that wish to implement a beneficial-use program need to address publicconcerns and provide assurances that the new uses of sludge and wastewater do not endangerhealth or the environment in application areas. The public and local officials should be involved inthe decision-making process at an early stage.

• The operators of municipal wastewater treatment facilities and the parties using sludge andwastewater should implement visible, stringent management and self-regulation measures,including monitoring and reliable reporting by farmers, and should support vigilant enforcementof appropriate regulations by local or state agencies. Implementation of these measures will becredible means of preventing nuisance risks and harm to people, property, and highly valuednearby resources.

• The municipal utility should carry out demonstration programs for public education, and to verifythe effectiveness of management and self-regulatory systems. In addition, the utility should beprepared to indemnify farmers against potential liabilities when farmers' financing by banks orother lenders may hinge on this assurance.

Other Regulations and Institutional Controls

From a regulatory perspective, it is important to remember that EPA's Part 503 Sludge Rule augments a widearray of existing institutional programs and controls over the disposition of municipal wastewater and sludge. Forexample, federal and state regulations govern the handling and treatment of toxic waste and the protection ofsurface and ground waters. These regulatory mandates appear adequate to manage most of the risks associatedwith land application, but they must be funded and implemented to be meaningful safeguards.

Sludges that do not meet beneficial use criteria standards as defined by the Part 503 Sludge Rule must bedisposed of according to federal and state regulations as applicable. Both the general public and state and localregulators should be aware that the Part 503 Sludge Rule is not the only control over agricultural use of sewagesludge.

Recommendation

• Management of sludge for beneficial use should be more visibly linked to existing regulationsgoverning its disposal. Program credibility may be improved and public concern reduced iffederal, state, and municipal


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regulators clearly assign authority to local governments for responding to any reports of adverseconsequences related to beneficial use of sludge, such as ground water contamination, odor,attraction of vermin, or illnesses. The public should be aware that state and local units ofgovernment have the necessary regulatory authority to take corrective actions against parties whohave violated rules and guidance.

CONCLUDING REMARKS

In summary, society produces large volumes of treated municipal wastewater and sewage sludge that must beeither disposed of or reused. While no disposal or reuse option can guarantee complete safety, the use of thesematerials in the production of crops for human consumption, when practiced in accordance with existing federalguidelines and regulations, presents negligible risk to the consumer, to crop production, and to the environment.Current technology to remove pollutants from wastewater, coupled with existing regulations and guidelinesgoverning the use of reclaimed wastewater and sludge in crop production, are adequate to protect human healthand the environment. Established numerical limits on concentration levels of pollutants added to cropland bysludge are adequate to assure the safety of crops produced for human consumption. In addition to health andenvironmental concerns, institutional barriers such as public confidence in the adequacy of the regulatory systemand concerns over liability, property values, and nuisance factors will play a major role in the acceptance of treatedmunicipal wastewater and sewage sludge for use in the production of food crops. In the end, these implementationissues, rather than scientific information on the health and safety risks from food consumption, may be the criticalfactors in determining whether reclaimed wastewater and sludge are beneficially reused on cropland.

The use of wastewater and sludge in the production of crops for human consumption presents a manageablerisk. However, the implementation of regulations and guidelines is where problems are most likely to arise.Municipal wastewater treatment plants, private processors, distributors, and applicators must not only comply withall regulatory requirements and management practices, they must take extra steps to demonstrate to variousstakeholders (e.g., neighbors, farmers, food processors, and consumers) that such compliance is occurring. Thismust be done through full public participation opportunities, self-monitoring and reporting programs, and publiceducation campaigns. This is particularly true if monitoring by state or local entities is likely to be minimal.General acceptance of sludge application for food crop production probably hinges most on the development ofsuccessfully implemented projects that meet state and federal regulations and address local public concerns.


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1

Introduction

Municipal wastewater treatment processes used in the United States were designed to receive raw municipalwastewaters from both domestic and industrial sources and produce a liquid effluent of suitable quality that can bereturned to natural surface waters with a minimal impact to the environment or to public health. A byproduct ofthis process, called sludge or sewage sludge, contains the solid fraction from the raw wastewater and the solidsproduced during the wastewater treatment processes. Both the effluent and sludge are treated to quality levelssuitable for disposal or recycling purposes. As described in Chapter 3, secondary treatment is the national standardfor discharge to surface waters (although local conditions can dictate either higher or lower treatment dependingon the assimilative capacity of receiving waters). When treated to acceptable levels or by appropriate processes tomeet state water reuse requirements, the effluent is generally referred to as ''reclaimed water." In an effort todistinguish sewage sludge that is treated and managed for beneficial purposes, the wastewater treatment industrynow refers to sewage sludge as "biosolids." However, for the purposes of this report, it is called "sewage sludge,"or simply "sludge." The rising volume of municipal wastewater, propelled by growing population and urbanization(see Figure 1.1), has inevitably increased the volume of treated effluent and treated sludge. During the pastdecades, some disposal practices have been restricted. Landfill space is scarce, sitings of incineration facilities aredifficult, and certain types of surface waters are adversely impacted by excess nutrient load and contaminants fromtreated effluents. Because of the wide range of environmental and societal problems associated with municipalwastewater and sludge disposal, municipalities have a need to find new ways to dispose of—or better, make useof—these materials. For coastal cities in particular, regulations requiring elimination of ocean disposal of sludgehave precipitated the need for other management alternatives.

Fortunately, these materials have the potential for use in agriculture. The simultaneous increase in the demandfor water, coupled with tighter regulation over the safety of sludge, widens an opportunity to use treated effluentfor irrigation, and to use treated sludge as a supplemental source of fertilizer and soil conditioner. The similaritiesof effluent to irrigation water and of sludge to fertilizer are further described in Chapter 2 (see Tables 2.1 and 2.2).Capturing and reusing the water and nutrient value of these materials help to conserve resources.

However, a pressing question is whether the use of these materials in an agricultural setting

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FIGURE 1.1 Increasing proportion of the U.S. population served by publicly owned treatment works (POTWs).SOURCE: EPA, 1995.

is safe and practical. Further, is it safe in all climates, on all soils, and is it sustainable over the long term?Because human health is inevitably the leading criterion for safety, the severest test is whether treated effluentsand treated sludge can be safely applied to crops that people eat.

The answer to whether wastewater and sludge can be safely applied to crops that people eat depends onseveral factors. These include the nature and amounts of potentially toxic or pathogenic constituents in treatedeffluents and sludges, the fate of these constituents once the materials are applied to an agricultural site, thepotential of harmful constituents to migrate into plant tissue, the potential for other environmental impacts onwater resources from runoff or infiltration, and whether long-term effects on the environment or future cropproduction are likely. An important safety consideration is the capability of facilities to produce treated effluentand treated sludge of consistent and reliable quality.

After safety, feasibility will govern the use of these materials in crop production. The distance of agriculturalfields from the treatment plants and competition with other effluent and sludge uses or disposal practices mayaffect the practicality of agricultural use. A critical consideration is whether the recipients of and those affected byrecycled effluents and sludge—farmers and their neighbors, the food processing industry, and consumers—willgive more weight to the benefits or to the risks of applying these materials to agricultural land.

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Irrigation of citrus trees with reclaimed water at the Water Conserv II reclamation project serving the City of Orlandoand Orange County, Florida (courtesy of Tom Lothrop, City of Orlando Environmental Services Department).

REFERENCE

EPA. 1995. Impacts of Municipal Wastewater Treatment: A retrospective analysis. Washington, D.C.: U.S. Environmental Protection Agency,Office of Water.

INTRODUCTION 16

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2

Municipal Wastewater, Sewage Sludge, and Agriculture

HISTORICAL PERSPECTIVES

Wastewater

Large-scale cropland application of municipal wastewater was first practiced about 150 years ago after flushtoilets and sewerage systems were introduced into cities in western Europe and North America. The wastewaterwas discharged without any treatment, and receiving watercourses became heavily polluted. The problem isillustrated by the situation in London in the 1850s when the "stink" from the River Thames obliged the House ofParliament to drench their drapes in chloride of lime (Snow, 1936). Water supplies drawn from the river below thesewage outfall were found by Dr. John Snow to be the source of the cholera outbreaks of the period. The partialsolution to the problem was the construction by Sir John Bazalgete of a vast interceptor along the north bank of theRiver Thames, creating the famed Thames Embankment. This gave relief to central London, but moved thepollution problem downstream. Sir Edwin Chadwick, a lawyer and crusader for public health at the time, was astrong advocate of separate sanitary sewers, and he coined the slogan, "the rain to the river and the sewage to thesoil." In this spirit, and to reduce pollution of the Thames downstream, "sewage farms" were established to takethe discharges from the interceptor. The agricultural benefits from the farms were incidental to their service in thedisposal of the wastewater.

The practice of sewage farms quickly spread. By 1875, there were about 50 such farms providing landtreatment in England, and many similar farms served major cities in Europe. By the turn of the century, there wereabout a dozen sewage farms in the United States. However, the need for a reliable outlet for wastewater was notentirely compatible with the seasonal nature of nutrient and water requirements of crop production. While sewagefarms alleviated pollution in the receiving streams, they created a different set of environmental sanitationproblems. Hydraulic and pollutant overloading caused clogging of soil pores, waterlogging, odors, andcontamination of food crops. The performance improved over the years as operators gained experience withbalancing the needs of wastewater disposal and crop growth. Nevertheless, the farms were gradually phased outwhen the land areas required to accommodate wastes from large cities grew too great to be practical and moreeffective technologies were developed to remove

MUNICIPAL WASTEWATER, SEWAGE SLUDGE, AND AGRICULTURE 17

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pollutants from wastewater. The processes of primary sedimentation and secondary biological treatment, whichwere developed in the early part of this century, required much smaller areas for their operations and were capableof producing clarified effluents for direct discharge into a surface water body. These technologies eliminated theneed for sewage farms.

In the United States, an estimated 0.69 m3 (182 gal) per capita per day of municipal wastewater is generated(Solley et al., 1993). Municipal wastewater treatment plants (otherwise known as publicly-owned treatment worksor "POTWs") currently serve around 75 percent of the U.S. population (EPA, 1995). The remainder are largelyserved by individual household septic systems. For those served by centralized facilities, the municipal wastewateris collected through a sewer network and centrally treated in a wastewater treatment plant. The collectedwastewater contains pollutants originating from households, business and commercial establishments, andindustrial production facilities. The general composition of municipal wastewater is well understood. For thepurpose of water-quality management, pollutants in municipal wastewater may be classified into the following fivecategories:

• Organic matter (measured as biochemical oxygen demand or BOD),• Disease-causing microorganisms (pathogens),• Nutrients (nitrogen and phosphorus),• Toxic contaminants (both organic and inorganic), and• Dissolved minerals.

Although the exact composition may differ from community to community, all municipal wastewatercontains constituents belonging to the above categories. Pollutants belonging to the same category exhibit similarwater quality impacts. The objective of wastewater treatment is to remove pollutants so that the effluent meets thewater quality requirement for discharge or reuse.

In modern society, thousands of potentially hazardous chemicals are used in household products andcommercial and industrial activities. They may be inadvertently or intentionally discharged into the wastewatercollection system. Municipal wastewater also contains many types of infectious, disease-causing organisms thatoriginate in the fecal discharge of infected individuals.

In wastewater treatment, the physical and chemical state of pollutants determine the approaches that areemployed to remove impurities. For this purpose, pollutants may be further classified (as per Camp and Messerve,1974) into:

• Settleable impurities,• Suspended impurities,• Colloidal impurities, and• Dissolved impurities.

Pollutants sharing the same physical state behave similarly during conventional wastewater treatment.With more than one hundred years of continuous development, municipal wastewater treatment technology in

use today can achieve almost any degree of treatment and removal of


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impurities desired. The conventional municipal wastewater treatment system consists of a series of processes,through which pollutants are removed, step by step, from the water and are concentrated into the solid fraction orsludge (see Chapter 3 for a further description of municipal wastewater and sludge treatment).

Treated effluents are customarily discharged into a surface water body. With advances in wastewatertreatment technology, wastewater effluents can achieve consistently high quality and are increasingly reclaimedfor reuse. The value of reclaimed water in crop irrigation has long been recognized, particularly where fresh waterresources are limited (Webster, 1954; Mertz, 1956; Sepp, 1971). Some wastewater reclamation programs (e.g., inFlorida) are also motivated by the need to avoid nutrient overload to sensitive receiving waters. In these cases,beneficial reuse can be more economical and/or technically feasible than employing the advanced wastewatertreatment needed to meet the requirements for surface water disposal.

In the United States, irrigating crops with reclaimed wastewater has been generally well accepted, both in thesemiarid western states and in Florida. The suitability of water for reuse is influenced by the chemical compositionof the source water, mineral pickup due to water use, and the extent of wastewater treatment. These characteristicsvary seasonally and from one municipality to another (Pettygrove and Asano, 1985). Dowdy et al. (1976) derived a"typical" chemical composition of treated wastewater effluent from a selected number of cities. This "typical"composition is compared to that of water from the Colorado River—a source for crop production in severalwestern states—for many of the water quality criteria important in irrigation (Table 2.1). Judged against existingguidelines for irrigation water quality criteria (National Academy of Sciences, 1973; Westcot and Ayers, 1985),the chemical composition of treated wastewater effluents, although widely varied, is acceptable for crop irrigation.In addition, treated effluents contain significantly higher amounts of nitrogen and phosphorus—fertilizer elementsessential for plant growth.

There are numerous examples of successful agricultural reuse projects in the United States. The wastewaterfrom Bakersfield, California has been used for irrigation since 1912 when raw sewage was used (Pettygrove andAsano, 1985). Currently, reclaimed water from Bakersfield irrigates approximately 2,065 ha (5,100 acres) of corn,alfalfa, cotton, barley, and sugar beets productions with more than 64,000 m3/day (16.9 million gal/day) ofprimary and secondary effluents from three treatment plants (Pettygrove and Asano, 1985). To avoid wastewaterdischarge to sensitive receiving waters, the city of Tallahassee, Florida has been using treated effluent foragricultural irrigation on city-owned farmland since 1966. About 68,000 m3/day (18 million gal/day) of secondaryeffluent are pumped approximately 13.7 km (8.5 miles) and irrigate about 700 ha (1,729 acres) (Roberts andBidak, 1994).

A seven-year agricultural wastewater reclamation demonstration study was conducted at Castroville,California, and completed in 1987. This study used a wastewater treatment process of secondary (biological)treatment, coagulation, filtration, and disinfection, with the final effluent meeting a quality standard of 2.2 totalcoliform/100 ml (the standard enforced by California's regulations for wastewater reclamation). The studyconcluded that the treatment process was acceptable for the spray irrigation of food crops to be eaten raw (Sheikhet al., 1990). The study detected no pathogenic organisms in the treated effluent, and spray irrigation with thetreated effluent did not adversely affect soil permeability, did not result in heavy metal accumulation in the soil orplant tissue, and did not adversely affect crop yield, quality, or shelf


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TABLE 2.1 Composition of Secondary Treated Municipal Wastewater Effluents and Irrigation Water

Secondary Effluenta

Parameter Range Typical Colorado Riverb Irrigation Water Quality Criteriac

Total Solids U 425 U NA

Total Dissolved Solids 200–1300 400 668.0 <2000

pH 6.8–7.7 7.0 7.9 6.5–8.4

Biochemical Oxygen Demand 2–50 25 U NA

Chemical Oxygen Demand 25–100 70 U NA

Total Nitrogen 10–30 20 U <30

Ammonia Nitrogen 0.1–25 10 U NA

Nitrate Nitrogen 1–20 8 0.1–1.2 NA

Total Phosphorus 5–40 10 <0.02 NA

Chloride 50–500 75 55–77 <350

Sodium 50–400 100 71–97 <70

Potassium 10–30 15 4–6 NA

Calcium 25–100 50 66–163 NA

Magnesium 10–50 20 23–28 NA

Boron 0.3–2.5 0.5 0.10–0.54 <3.0

Cadmium (ug/L) <5–220 <5 <1–69 10

Copper (ug/L) 5–50 20 <10–10 200

Nickel (ug/L) 5–500 10 <1–4 200

Lead (ug/L) 1–200 5 <5 5000

Zinc (ug/L) 10–400 40 <3–12 2000

Chromium (ug/L) <1–100 1 <1 100

Mercury (ug/L) <2–10 2 <0.1–0.1 NA

Molybdenum (ug/L) 1–20 5 2–8 10

Arsenic (ug/L) <5–20 <5 4–16 100

All units in milligrams per liter unless otherwise noted as micrograms per liter (ug/L). U: unavailable. NA: not applicable.a Adapted from Asano et al., 1984 and Treweek, 1985b Radtke, et al., 1988c from Westcot and Ayers, 1985 and National Academy of Sciences, 1973


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life. Over a 10-year period, Yanko (1993) assayed 590 filtered and chlorine-treated secondary effluentsamples from wastewater treatment plants in Los Angeles County for enteric viruses. All of the effluent sampleshad met California's wastewater reclamation standard of 2.2 coliform/100 ml, and only one was found positive forvirus (Coxsackie B3).

State regulations of the use of reclaimed wastewater on food crops are aimed at protecting consumers frompossible exposure to pathogens (discussed in Chapter 7). The potential health hazard of trace elements (includingheavy metals) and toxic organic chemicals has been addressed for a variety of end used of reclaimed wastewater,but they have not been regulated for purposes of agricultural irrigation. As mentioned, concentrations of traceelements in wastewater effluents that have undergone secondary or higher levels of treatment are normally withinexisting guidelines for irrigation water quality criteria (see Chapter 4 for a discussion of trace elements and organicchemicals).

Sewage Sludge

Before the era of wastewater treatment, municipal wastewater was untreated and sludge did not exist. Sewagesludge is an end product of municipal wastewater treatment and contains many of the pollutants removed from theinfluent wastewater. Sludge is a concentrated suspension of solids, largely composed of organic matter andnutrient-laden organic solids, and its consistency can range in form from slurry to dry solids, depending on thetype of sludge treatment. Agricultural utilization of sewage sludge has been practiced since it was first produced.Given agricultural experience with the use of human excrement, sewage, and animal manure on croplands, theapplication of municipal wastewater sludge to agricultural lands was a logical development. As an early example,municipal sludge from Alliance, Ohio was used as a fertilizer as early as 1907. During the same period, Baltimore,Maryland used domestic septage in agricultural production (Allen, 1912). The plant nutrient value of sludge hasbeen evaluated by many investigators (Rudolfs and Gehm, 1942; Sommers, 1977; Tabatabai and Frankenberger,1979), and the nutrient composition is considered to be similar to other organic waste-based soil amendments thatare routinely applied on cropland, such as animal manures (as shown in Table 2.2). In addition to major plantnutrients, sludge also contains trace elements that are essential for plant growth. Soils which have been tilled fordecades are often deficient in certain trace elements, such as zinc and copper (Martens and Westermann, 1991).Certain calcareous soils are deficient in iron (Martens and Westermann, 1991). Land applications of municipalsludge can help to remedy these trace metal deficiencies (Logan and Chaney, 1983).

Early agricultural sludge use projects were often carried out with little regard for possible adverse impacts tosoil or crops (Allen, 1912). A common goal was to maximize the application rate to minimize the cost of sludgedisposal. Since the early 1970s, more emphasis has been placed on applying sludge to cropland at an agronomicrate (Hinesly et al., 1972; Kirkham, 1974).

Wastewater treatment authorities attempt to manage the volume of wastewater and type of pollutantsdischarged into sewers to protect the integrity of the infrastructure, health and well-being of sanitation workers, theperformance of wastewater treatment processes, and the impact on receiving waters. Federal and state regulationsexert control over the quality of the treated


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effluent in order to keep contaminants below concentrations that would be harmful to humans and theenvironment.

TABLE 2.2 Chemical Composition of Sewage Sludge and Animal Manure

Constituent (Unit) Animal Manurea Sewage Sludge

Range Range Typical

Nitrogen (% dry weight) 1.7–7.8 <0.1–17.6b 3.0

Total phosphorus (% dry weight) 0.3–2.3 <0.1–14.3b 1.5

Total sulfur (% dry weight) 0.26–0.68 0.6–1.5b 1.0

Calcium (% dry weight) 0.3–8.1 0.1–25b 4.0

Magnesium (% dry weight) 0.29–0.63 0.03–2.0b 0.4

Potassium (% dry weight) 0.8–4.8 0.02–2.6b 0.3

Sodium (% dry weight) 0.07–0.85 0.01–3.1b -

Aluminum (% dry weight) 0.03–0.09 0.1–13.5b 0.5

Iron (% dry weight) 0.02–0.13 <0.1–15.3b 1.7

Zinc (mg/kg dry weight) 56–215 101–27,800b 1200

Copper (mg/kg dry weight) 16–105 6.8–3120c 750

Manganese (mg/kg dry weight) 23–333 18–7,100b 250

Boron (mg/kg dry weight) 20–143 4–757b 25

Molybdenum (mg/kg dry weight) 2–14 2–976b 10

Cobalt (mg/kg dry weight) 1 1–18b 10

Arsenic (mg/kg dry weight) 12–31 0.3–316c 10

Barium (mg/kg dry weight) 26 21–8,980b -

a Data summarized from Azevado and Stout, 1974b Data summarized from Dowdy et al., 1976c Data summarized from Kuchenrither and Carr, 1991

Nevertheless, toxic chemicals in low concentrations are introduced into municipal wastewater. Many of thesetoxic chemicals are removed from the wastewater and concentrated into the sewage sludge by the wastewatertreatment process. Sewage sludge also contains human pathogens, although it can be treated to significantly reducethe number of pathogens present. Pathogens and toxic chemical pollutants may be introduced into sludge-amendedsoil.


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Since about 1970, there has been an intense and concerted effort of scientific research world-wide to betterunderstand the fate of potentially toxic and pathogenic constituents in sludge when sludge is applied toagricultural soils. A search of agricultural research articles (from the computer database, AGRICOLA) revealedmore than 2,300 articles published since 1970. The surge of technical information regarding agriculturalapplication of sewage sludge has led to the development of pollutant loading guidelines by the United States andwestern European countries (McGrath et al., 1994). The World Health Organization is also investigating ways todevelop human health-related chemical guideline for using treated municipal wastewater effluents and sewagesludge in agriculture production (Chang, et al., 1993).

Since the late 1970s and early 1980s, source control and industrial wastewater pretreatment programs havebeen initiated to limit the discharge of industrial pollutants into municipal sewers, and these programs haveresulted in a dramatic reduction of toxic pollutants in wastewater and in sludge (see Chapter 3 for a discussion ofindustrial pretreatment). Municipal wastewater sludge, particularly from industrialized cities, now has significantlylower levels of toxic contaminants—specially heavy metals—than in earlier decades when much of the research onsludge application to cropland was conducted. Tables 2.3, 2.4, and 2.5 show decreasing levels of metals inwastewater or sludge for municipal sewage treatment facilities in Chicago, Baltimore, and Philadelphia fromabout 1970 through 1985. More recently, a comparison of sludge quality was made between two EPA surveys(Kuchenrither and McMillan, 1990): a study of 40 cities conducted in the late 1970's (EPA, 1982) and theNational Sewage Sludge Survey (NSSS) conducted in the late 1980s (EPA, 1990). While the two studies useddifferent sampling and analytic techniques, the comparison (in Table 2.6) shows that most metals havesignificantly lower concentrations in the NSSS than in the 40-city study, largely as a result of industrialpretreatment programs. The data on organic compounds is difficult to compare as the limits of detection betweenthe two studies varied. EPA's 1991 report to Congress (EPA, 1991) also documents a reduction in sludge metalconcentrations from about 1985 to 1990 in a number of POTWs across the country.

For a long time, wastewater treatment authorities in the United States managed land applications of sewagesludge with little governmental attention. Early regulations governing sewage sludge disposal were developed bystate public health agencies with the intention of controlling infectious disease. Although federal guidelines forland application of sewage sludge were proposed as early as 1974, comprehensive federal regulations did not existuntil 1993. EPA first developed sludge management regulations under the 1972 Federal Water Pollution ControlAct to prevent sludge-borne pollutants from entering the nation's navigable waters. In 1977, Congress amended theAct to add a new section, 405(d), that required EPA to develop regulations containing guidelines to (1) identifyalternatives for sludge use and disposal; (2) specify what factors must be accounted for in determining the methodsand practices applicable to each of these identified uses; and (3) identify concentrations of pollutants that wouldinterfere with each use. In 1987, Congress amended section 405 again and established a timetable for developingsewage sludge use and disposal guidelines. Through this amendment, Congress directed EPA to: (1) identify toxicpollutants that may be present in sewage sludge in concentrations that may affect the public health and theenvironment and (2) promulgate regulations that specify acceptable management practices and numericalconcentration limits for these pollutants in sludge.


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TABLE 2.3 Metal Loadings in Raw Wastewater (in kg/day) Entering the Chicago Area Treatment Facilities in Response toPretreatment Programs

Cd Cr Cu Pb Ni Zn

1971 398 5,197 2,166 2,049 2,443 6,972

1972 343 3,321 1,996 1,793 1,377 4,641

1973 301 2,463 961 1,063 957 4,260

1974 213 1,894 652 735 643 3,403

1975 113 1,522 538 497 386 2,537

1976 132 1,527 685 368 416 2,400

1977 168 1,422 588 536 436 2,587

1984 121 1,185 949 396 702 2,322

Note: Table 2.3 combines data from two different POTWs within the Metropolitan Sewerage District of Greater Chicago. Pretreatmentprograms began in 1972.SOURCE: Adapted from Page et al., 1987.

The intent of the 1987 amendment was to ''adequately protect human health and the environment from anyreasonably anticipated adverse effect of each pollutant" [Section 405 (d)(2)(D)]. Section 405 also states that anypermit issued to a POTW or other treatment works for wastewater discharge should specify technical standards forsludge use or disposal. The Standards for the Use and Disposal of Sewage Sludge, Code of Federal Regulations,Title 40, Part 503 (EPA, 1993) were promulgated in 1993, and are collectively referred to in this report as the"Part 503 Sludge Rule."

IRRIGATION WITH RECLAIMED WATER

Crop Irrigation

The nation encompasses 930.8 million hectares (2,300 million acres) of land, of which 125 million hectares(309 million acres), or 14 percent were used to grow crops in 1993 (USDA, 1992). Figure 2.1 shows theproportion of cropland devoted to different categories of crops. The category "fresh food" includes such producecrops as broccoli, potatoes, or fruit that are bought and consumed fresh, and this is the smallest category in termsof total acreage. Other food crops, such as small grains, vegetables used for commercial processing (canning andprocessing), peanuts, sugar beets, and sugar cane, are grown on roughly 24 percent of cropland. Crops fordomestic animal consumption—feed and hay—occupy the bulk of cropland. Farmers


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TABLE 2.4 Metal Concentrations in Digested Sludge Filter Cake (in mg/kg dry weight) at the Back River POTW,Baltimore, Maryland in Response to Pretreatment Programs

Year Cd Cu Pb Ni Zn

1978 51 2,750 680 423 5,000

1979 23 2,540 539 397 3,540

1980 18 2,840 433 381 3,400

1981 19 2,070 493 374 3,410

1982 18 1,110 398 193 2,360

1983 23 1,060 324 214 2,620

1984 26 1,010 372 266 2,750

1985 22 681 346 126 2,030

Note: Source identification began in 1980 and source reduction began in 1981. Based on monthly composites in early years, then biweeklyand weekly.SOURCE: Adapted from Page et al., 1987.

often practice crop rotation, so a variety of crops may be grown on the same piece of land over a period ofseveral years.

Irrigated crop production expanded in the United States from nearly 7.7 million hectares (19 million acres) in1945 to more than 20.5 million hectares (51 million acres) in 1978. The total amount of irrigated cropland droppedby 1987 to 18.8 million hectares (46 million acres) (Figure 2.2, Council for Agricultural Science and Technology,1992; USDA, 1992). About 15 percent of harvested crops are grown on the 5 percent of farmland that is irrigated.Irrigation is essential in semiarid and arid regions to produce of many crops including orchard crops, andvegetables (Figure 2.3). Irrigated crops represent 38 percent of the total revenue from crop production in theUnited States (Bajwa, et al. 1992).

Deemand for Irrigation Water

Much of the nation's water withdrawal is used for crop irrigation. In 1990, crop irrigation accounted for 518million m3/day (137,000 million gal/day) of water or 41 percent of all fresh water withdrawn for all uses fromwell and surface water (Solley et al., 1993). Irrigation is also a highly consumptive use of water; about 56 percentof the quantity withdrawn is lost to evaporation and plant transpiration, and so is not available as return-flow tosurface waters. By comparison, domestic, commercial, industrial and mining uses consume an average of 17percent of the water withdrawn for these purposes.


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TABLE 2.5 Metal Concentrations in Sludges (in mg/kg dry weight) at Two Philadelphia Wastewater Treatment Plants inResponse to Pretreatment Programs

Year Cd Cu Pb Ni Zn

Southwest

1974 31 825 1,540 100 3,043

1976 27 1,110 2,710 103 2,650

1977 27 1,400 2,170 185 3,940

1978 16 1,020 1,800 275 4,050

1980 18 986 740 98 2,780

1981 25 971 562 117 2,300

1982 20 940 1,030 113 2,440

1983 12.5 736 421 79 1,700

1984 14.3 1,140 427 111 1,830

1985 15.0 880 373 80 1,730

Northeast

1974 108 1,610 2,270 391 5,391

1976 97 2,240 2,570 372 5,070

1977 71 2,320 2,680 459 3,920

1978 57 1,240 1,620 319 5,910

1980 26 1,210 728 275 3,890

1982 14 985 423 185 2,570

1983 10.9 1,020 351 130 2,110

1984 12.4 1,200 360 130 1,980

1985 17.3 1,270 382 187 2,100

Note: Source identification began in 1976. Liquid sludge analyzed until 1982, and sludge filter cake from 1983 on.No data available for 1975 and 1979.SOURCE: Page et al., 1987.


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TABLE 2.6 Comparison of Organics and Trace Elements From the 40-Cities Study Conducted in the Late 1970s and theNational Sewage Sludge Survey (NSSS) Conducted in the Late 1980s

Organic Pollutants (µg/kg, unless noted by * = mg/kg) Percent Detection Mean Values

40 Cities NSSS 40 Cities NSSS

Aldrin 16 3 6.4 1.9

Benzene 93 0 1782 —

Benzo(a)pyrene 21 3 138 —

Bis(2-ethylhexyl)phthalate 100 62 155* 74.7*

Chlorodane 16 0 6.4 —

Dieldrin 16 4 6.4 —

Heptachlor 16 0 6.4 —

Hexachlorobenzene 16 0 155 —

Hexachlorobutadiene 5 0 23 —

Lindane 16 0 6.4 —

Dimethylnitrosamine 5 0 57 —

PCB's N/A N/A — —

Toxaphene 16 0 6.4 —

Trichloroethene 84 1 8139 —

DDD/DDE/DDT N/A N/A — —

Trace Elements(mg/kg, values in O denote composited means by mass in NSSS)

Arsenic 100 60 6.7 9.9 (10)

Beryllium 100 23 1.67 0.4 (1)

Cadmium 100 69 69.0 7.0 (22)

Chromium 100 91 429 119 (268)

Copper 100 100 602 741 (730)

Lead 100 80 969 134 (205)

Mercury 100 63 2.8 5.2 (3)

Molybdenum 75 53 17.7 9.2 (11)

Nickel 100 66 135.1 42.7 (70)

Selenium 100 65 7.3 5.2 (5)

Zinc 100 100 1594 12 (1550)

SOURCE: EPA, 1990.


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FIGURE 2.1 The proportion of U.S. cropland devoted to different crops. Categories defined by U.S. Department ofAgriculture.SOURCE: USDA, 1992.

FIGURE 2.2 The expansion and also, in four regions, the contraction of irrigated area of the United States.SOURCE: Council for Agricultural Science and Technology, 1992.


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FIGURE 2.3 Irrigated acreage of principal crops in the United States and the percentages of total crop acreage that isirrigated.SOURCE: Bajwa et al., 1992.

Reclaimed wastewater provides a very small volume of the nation's crop irrigation water although it is asignificant source of water in some areas. Nationally, the United States produces 134 million m3/day (35,400million gal/day) of municipal wastewater. Approximately 3 percent of this quantity, or 3.5 million m3/day (925million gal/day), is reclaimed (Solley et al., 1993). About 70 percent of this reclaimed water goes towardsirrigation, but the national estimates do not distinguish between urban and agricultural irrigation. In Florida,agricultural irrigation accounts for approximately 34 percent of the total volume of reclaimed water used withinthe state (Florida Department of Environmental Regulation, 1992). In California, agricultural irrigation accountsfor approximately 63 percent of the total volume of reclaimed water (California State Water Resources ControlBoard, 1990). Even so, only 5 percent of California's reclaimed water irrigates land used to grow crops classifiedfor human consumption (Figure 2.4, EPA, 1992). It is probable that reclaimed water accounts for less than 0.5percent of the water used nationally for agricultural irrigation.

Although the total volume of treated wastewater produced in the United States could theoretically satisfy 26percent of the need for agricultural irrigation, this magnitude of reuse is not likely. The volume of wastewaterproduced by a community does not often match the volume of water needed for crop irrigation in the nearbyvicinity. In fact, much of the wastewater in the United States is produced in areas where crop irrigation is notneeded or is only occasionally required. Figure 2.5 shows the distribution of U.S. irrigated agriculture andTable 2.7 illustrate regional imbalances in irrigation needs relative to the amount of wastewater produced. For thepurpose of Table 2.7, the 18 water resource regions defined by U.S. Water Resources Council (Solley et al., 1993)have been simplified to six (Figure 2.6).

The Northeast region has about half of the population of the U.S. and produces about half


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FIGURE 2.4 Proportion of different crop types irrigated by reclaimed water in California.SOURCE: California State Water Resources Control Board, 1990.

FIGURE 2.5 The distribution of irrigated agriculture in the United States.SOURCE: Bajwa et al., 1992.


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TABLE 2.7 Relation of Reclaimed Water Generated to Agricultural Needs by Region

Region Wastewater Return Flow(bgd)a

Reclaimed Water Water Drawn forAgricultural Irrigation(bgd)

Reclaimed Water as aPercent of Water Drawnfor Agriculture Irrigation

Percent bgd

Northeast 20.0 0.3 0.06 1.0 6.0

Southeast 6.0 4.6 0.276 17.0 1.6

California 3.0 8.5 0.255 28.0 0.9

Great Plains 2.3 1.0 0.023 38.0 0.06

Northwest 2.2 0.5 0.011 32.0 0.03

Southwest 1.1 26.2 0.288 19.0 1.5

a billion gallons per daySOURCE: Derived from information in Solley, et al., 1993.

of the wastewater. This region has a relatively short growing season and a humid-climate; thus the demandfor crop irrigation is low. In all other regions, the amount of water required by irrigation far exceeds the volume ofwastewater produced (Solley, et al., 1993). Water conveyance is a significant cost of a water reuse project andeven in the semi-arid and arid western states, the distance between generators and potential users of reclaimedwater will determine its feasibility.

Wastewater Reclamation Motivated by Disposal Priorities

In 1976, the city of St. Petersburg, Florida initiated a wastewater reuse program which included diverting itstreated wastewater effluent to urban reuse purposes to avoid the pollution of Tampa Bay (EPA, 1992). It wasconsidered a pioneering effort then. It is interesting to note that the reclaimed water was initially not metered inSt. Petersburg; customers were urged to use as much as they wanted at a flat rate per acre. Currently, reclaimedwater is valued for its ability to reduce water demand, and meters are now being retrofitted. The publication ofQuality Criteria for Water (EPA, 1976) set minimum national in-stream water quality limits that includenumerical limits for metals and toxic organics. When effluents are discharged into a large or fast-flowing waterbody, the water quality standard can more easily be met because of the dilution that occurs in the receivingstream. However, POTWs that discharge into small or intermittent streams are not able to take advantage ofdilution, and their discharge limits may be as stringent as the in-stream water quality standards. In many cases, thelocal or state requirements are even more restrictive than the national requirements. Often, the pollutants ofconcern are nutrients such as phosphorus rather than toxic chemicals.

To meet these strict in-stream requirements, and to control treatment costs, many communities areconsidering water reuse to achieve regulatory compliance (Shacker and Kobylinski,


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FIGURE 2.6 Water resource regions referred to in Table 2.7. For purposes of Table 2.7, the 18 water resourceregions as established by the U.S. Water Resources Council have been simplified to six as follows: "Northeast"includes New England, Mid-Atlantic, Tennessee, Ohio, Great Lakes, Upper Mississippi, and Sorris-Red-Raineyregions; "Southeast" includes South Atlantic-Gulf, Lower Mississippi, and Texas-Gulf regions; "Southwest" includesLower Colorado, Upper Colorado, and Great Basin regions; "Great Plains" includes Missouri, Arkansas-White-Red,and Rio Grande regions; "Northwest '' is the Pacific Northwest region; and "California" is the California region.SOURCE: modified from Solley et al., 1993.

1994). Therefore, both water shortage and waste disposal are driving forces for the use of reclaimedwastewater, and the dominance of one over the other will depend on local conditions. A recent survey of waterreuse projects in California indicated that two thirds of the projects were initiated exclusively for water supplypurposes. Only 4 percent of the projects were motivated by the need for pollution control, and the rest were mixed(Water Reuse Association of California, 1993).

Miller (1990) found that urban landscape irrigation (e.g, for golf courses and highway median strips) is oneof the fastest growing uses of reclaimed wastewater in the United States In Florida, two-thirds of the reclaimedwater is used for urban landscape purposes (Paret and Elsner, 1993). The Irvine Ranch Water District in Californiairrigates about twice as much urban land as farmland, and the expectation is that water use on urban land willincrease as agricultural land is taken out of production and replaced by residential development (Parsons, 1990).Throughout California, nonagricultural use of reclaimed wastewater is expected to increase faster over the next 20years as achievement of state goals for water reuse is approached, and it is


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estimated that the proportion of reclaimed water for crop irrigation will shrink from 21 to 13 percent of allreclaimed water uses (Water Reuse Association of California, 1993).

Value of Reclaimed Wastewater

The costs to reclaim wastewater vary depending on the level of treatment required by state water reuseprograms. The total cost of reclaiming 1 acre-foot (1,233 m3) of municipal wastewater are estimated at roughly$500/acre-foot ($406 per 1,000 m3) in both Denver, Colorado and Orange County, California (Miller, 1990),which is roughly equivalent to the cost that southern California utilities pay to the Metropolitan Water District forimported water. The value of reclaimed water to the farmer will depend on its cost relative to other off-farm watersupplies. In 1988, the average cost to the farmer of an off-farm water supply in the United States was $34/acre-foot ($27.50 per 1,000 m3) and ranged from about $89/acre-foot ($72.10 per 1,000 m3) in Arizona to $1/acre-foot($0.81 per 1,000 m3) in Arkansas (1988 prices from Bajwa et al, 1992). These rates are considerably less than theamortized unit cost for developing and maintaining a water reclamation facility. If the farmers currently obtainirrigation water at low prices, they are not expected to pay more for using reclaimed water. In areas where themotivation for a water reclamation project is pollution abatement rather than water savings, reclaimed water islikely to have a low market value, and farmers may receive the treated effluent free of charge. In these situations,it may be more attractive for POTWs to seek other alternatives, such as reclaiming water for industrial users whoare paying higher water rates.

Treated effluent contains plant nutrients and has potential value as a fertilizer. Even so, the value of effluentas a fertilizer is not significant when total farm production costs are considered. Fertilizer comprised about 6percent of the $108 billion total production expenses of U.S. farming in 1987 (U.S. Bureau of the Census, 1990).Projected 1992 production costs for several high-value food crops predicted fertilizer costs ranging from 0.03 to11.5 percent (Table 2.8).

For crops to grow properly, the correct fertilizers must be applied at appropriate intervals in the appropriateamounts. When reclaimed water is used, irrigation needs rather than nutrient requirements may determinefertilizer inputs. The nutrients contained in the irrigation water may not be appropriate in terms of type, amounts,and timing. Effluent irrigation takes place during the warmest part of the season, and fertilization will occur eventhough fertilizer may only be needed during the early, cool part of the season. Heavy fertilization during the warmseason can encourage undesirable vegetative growth (Bouwer and Idelovitch, 1987).


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TABLE 2.8 The Cost of Fertilizer As a Percentage of All Costs for the Production of Some Food Crops

Crop Percent of Total Costs State

Fresh apples 0.6 Pennsylvania

Processing apples 1.3 Pennsylvania

Green tomatoes 2.4 California

Ripe tomatoes 2.6 Pennsylvania

Carrots 3.4 California

Fresh broccoli 4.1 California

Iceberg lettuce 4.9 California

Sweet corn 6.8 California

Tomatoes for processing 10.2 California

Potatoes 11.5 Pennsylvania

SOURCES: University of California Imperial County Cooperative Extension 1992; Harper, 1993.

USE OF SEWAGE SLUDGE IN AGRICULTURE

Potential Role of Sewage Sludge in Crop Production

Based on estimates of the amount of solids produced in typical primary and secondary wastewater treatmentprocesses (Metcalf and Eddy, 1991), the national production of sewage sludge is approximately 7 million metrictons/year. Secondary and higher levels of treatment account for 5.3 million metric tons/year, and the remaindercomes from coastal discharges and sewage ponds (EPA, 1993). The quantity of sewage sludge is expected toincrease as a greater percentage of the population is served by sewers and as advanced wastewater treatmentprocesses are brought on-line (refer back to Figure 1.1). Currently, 36 percent of sewage sludge is applied to theland for several beneficial purposes, such as agriculture, turfgrass production, or reclamation of surface miningareas. 38 percent is landfilled, 16 percent is incinerated, and the remainder is surface disposed by other methods(EPA, 1993). With the promulgation of the Part 503 Sludge Rule, EPA encouraged agricultural use of sewagesludge.

From a national perspective, sludge has very little impact on agriculture. If all sludge produced in the UnitedStates was used agriculturally and applied according to agronomic nitrogen requirements, it would only require anestimated 1.59 percent of the nation's cropland (assuming that the average concentration of available nitrogen inthe sludge is 4 percent dry weight and it is applied at 100 kg nitrogen/ha/yr).

Regional and local availability of farmland will, however, affect the potential for increased agricultural use oftreated municipal sludge. The ratio of available farmland to sludge produced is an initial consideration inagricultural use of sludge. North Dakota, for example, would require only 0.05 percent of its agricultural land totake up all sludge produced in the state at agronomic rates for nitrogen. The Madison Metro Sewerage District hasapplied anaerobically digested sludge to private farmland since 1974, and the demand for sludge outstrips


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the supply (Taylor and Northouse, 1992). Rhode Island, on the other hand, would need to utilize 100 percent of itscropland to use up its sludge supply; because that is unlikely, other use or disposal options are required. Table 2.9shows a comparison of the amounts of cropland required to accommodate in-state sludge applications atagronomic rates. Unlike wastewater effluents, sludge can be transported further distances. For example,contractors are currently shipping some of New York City's treated sludge to northeastern Texas and easternColorado for cropland application. Boston, Massachusetts ships a portion of its sludge in the form of heat-driedpellets to Florida for application to cropland and pastures. Some of the sludge from the Los Angeles Basin is beingtransported by truck for cropland application in Yuma, Arizona.

The cost of transporting sludge for land application must be weighed against the cost and environmentalconsequence of other sludge disposal options on a case by case basis. If wastewater treatment authorities in urbancenters cannot overcome the variety of obstacles to use sludge within reasonable transportation distances, theyface the consequences of long distance transportation and its associated costs. These geographical and economicalconstraints on land application create uncertainty over how much of the nation's sewage sludge will be applied oncropland in the long run.

From the farmer's perspective, other factors limit agriculture use of sewage sludge. Sewage sludge isinherently more difficult to use than chemical fertilizers. In part, this is because the composition of plant nutrientsand trace elements vary due to differences among types of sludges (e.g., different water contents or treatmentprocesses) and differences among municipalities and their industrial contributors. The composition of commercialfertilizers are formulated to meet crop requirements. Some have argued that any cost savings derived fromsubstituting sludges for chemical fertilizers may be insignificant (White-Stevens, 1977) and that unless the wastegenerators offer them payment, the financial incentive for farmers to apply sewage sludge to cropland may bemarginal. Others point out that sludge has significant nutrient value, which can range from $100 to $140 per acre(EPA, 1994), and that its effect on soil physical properties can increase crop yield (e.g., Logdson, 1993).Generally, the POTW makes arrangements for hauling and spreading sewage sludge on farmland.

Ecological Linkages Between Urban and Agricultural Systems

The land application of sewage sludge can ecologically link nutrient usage within urban and rural landscapes(Millner, 1994). If nutrients and organic matter are returned to agricultural soil via land application of sludges, theneed to supplement the agroecosystem in terms of nutrients will diminish. In this sense, cropland recycling ofsewage sludge close to its urban source can conserve energy as does the recycling of crop residues and farmanimal manures.

In natural ecosystems, the external inputs to primary food production are solar energy and water (Figure 2.7).Natural ecosystem productivity is sustained through the recycling of nutrients extracted by primary producers(plants) and made available again in the process of organic matter mineralization. In contrast, conventional cropproduction is enhanced by external inputs of energy, water, nutrients, and chemical herbicides and pesticides(Figure 2.7). The capacity of modern agroecosystems for natural feedback and regulation has been greatly reducedin order to increase crop yields (Risser, 1985; Barrett et al., 1990). When these external inputs


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TABLE 2.9 Amount of Cropland Required to Accommodate In-state Sludge Applications at Agronomic Rates

State Populationa

(millions)SludgeProducedb

(thousands ofmetric tons)

CroplandRequiredc

(thousands ofhectares)

Croplandd


Percent of StateCropland

New England

Maine 1.24 24.78 9.91 158 6.3

New Hampshire 1.12 22.38 8.95 43 20.8

Vermont 0.57 11.39 4.56 177 2.6

Massachusetts 6.01 120.10 48.0 79 60.8

Rhode Island 1.00 19.98 7.99 8 100.0

Connecticut 3.27 65.35 26.1 62 42.1

Middle Atlantic

New York 18.70 363.63 149.4 1,539 9.7

New Jersey 7.87 157.27 62.9 166 37.9

Pennsylvania 12.05 240.80 96.3 1,716 5.6

East North Central

Ohio 11.10 221.82 88.7 3,921 2.3

Indiana 5.71 114.11 45.6 4,335 1.1

Illinois 11.70 233.81 93.5 8,162 1.1

Michigan 9.47 189.25 75.7 2,591 2.9

Wisconsin 5.04 100.72 40.3 3,339 1.2

West North Central

Minnesota 4.52 90.33 36.1 7,086

Iowa 2.81 56.15 22.5 8,359 0.51

Missouri 5.23 104.52 41.8 4,987 0.27

North Dakota 0.63 12.59 5.04 10,305 0.84

South Dakota 0.71 14.19 5.68 6,889 0.05

Nebraska 1.60 31.99 12.8 7,285 0.08

Kansas 2.53 50.58 20.2 10,433 0.18

South Atlantic

Delaware 0.70 13.99 5.6 202 2.8

Maryland 4.96 99.12 39.6 578 6.9

Dist. of Columbia 0.58 11.59 4.64 0 0.0

Virginia 6.49 129.69 51.9 1,081 4.8

West Virginia 1.82 36.36 14.5 274 5.3

North Carolina 6.94 138.69 55.5 1,647 3.4

South Carolina 3.64 72.74 29.1 786 3.7

Georgia 6.92 138.29 55.3 1,516 3.6

Florida 13.68 273.38 109.4 931 11.8


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State Populationa

(millions)Sludge Producedb

(thousands ofmetric tons)

CroplandRequiredc


Croplandd


Percent of StateCropland

East South Central

Kentucky 3.79 75.74 30.3 1,923 1.6

Tennessee 5.10 101.92 40.8 1,731 2.4

Alabama 4.19 83.73 33.5 959 3.5

Mississippi 2.64 52.76 21.1 1,635 1.3

West South Central

Arkansas 2.42 48.36 19.3 2,711 0.71

Louisiana 4.29 85.73 34.3 1,612 2.1

Oklahoma 3.23 64.55 25.8 3,871 0.67

Texas 18.03 360.31 144.1 7,911 1.8

Mountain

Montana 0.84 16.79 6.72 6,200 0.11

Idaho 1.10 21.98 8.79 2,065 0.43

Wyoming 0.47 9.39 3.76 870 0.43

Colorado 3.56 71.14 28.5 3,514 0.81

New Mexico 1.61 32.17 12.9 493 2.6

Arizona 3.93 78.54 31.4 427 7.4

Utah 1.86 37.17 14.9 517 2.9

Nevada 1.39 27.78 11.1 236 4.7

Pacific

Washington 5.25 104.91 42.5 2,701 1.6

Oregon 3.03 60.55 24.2 1,495 1.6

California 31.21 623.69 249.5 3,516 7.1

Alaska 0.60 11.99 4.8 13 36.9

Hawaii 1.17 23.38 9.35 66 14.2

a Estimate of July 1993 population from U.S. Census Bureau.b Sludge production estimates assume 75% of population is sewered and produces .073 kg of sludge per person per day.c State cropland required if all sludge produced in-state were to be applied at agronomic rates using the assumption of 4 percent availablenitrogen dry weight and an application rate of 100 kilograms per hectare per year.d 1987 land utilization from U.S. Department of Agriculture, 1992.

exceed the capacity of the agroecosystem to accommodate them, the result is an increase in system outputs ofboth natural and unnatural byproducts that can cause environmental harm. Society often bears the financial costsrequired to restore environmental quality and to maintain high crop yields.

Frequently, cropland is removed from crop production and permitted to lie fallow for several years. Thesefallow fields are often referred to as old-field communities or old-field ecosystems. Various studies on the effectsof sludge application to old-field ecosystems have focused on ecological trophic levels, including producers (Malyand Barrett, 1984; Hyder and


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FIGURE 2.7 Diagrams depicting a) natural, and b) human inputs into agroecosystems.SOURCE: Adapted from Barrett et al., 1990.

Barrett, 1986), primary consumers (Anderson and Barrett, 1982; Brewer et al., 1994), secondary consumers(Brueske and Barrett, 1991), detritivores (Kruse and Barrett, 1985; Levine et al., 1989) and decomposers (Suttonet al., 1991,; Brewer et al., 1994). Thus far, the research indicates that old-field ecosystems are ecologically safeand economically viable sites for sludge disposal (Maly and Barrett, 1984; Carson and Barrett, 1988; Levine et al.,1989; and Brewer


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et al., 1994). These old-fields may again revert to cropland usage due to improved productivity and soilconditioning.

SUMMARY

With continuing advancement in wastewater treatment technology and increasingly stringent wastewaterdischarge requirements, treated wastewater effluents produced by municipal treatment plants in the United Stateshave achieved consistent high water quality and are increasingly being considered for nonpotable reuse. In thesemiarid and arid western states, treated wastewater has been used as a new source of water to help alleviateshortages faced by water-deficient communities. More recently, the need to meet local minimum in-stream waterquality limits when treated effluents are discharged into surface water bodies has motivated many municipalities toconsider effluent irrigation.

The chemical composition of most treated effluents is within the range defined by accepted irrigation waterquality criteria and is comparable to that of water commonly used in crop and landscaping irrigation. At present,treated municipal wastewater probably accounts for much less than one percent of national irrigation waterrequirements, and it is likely that the level of agricultural use will not significantly increase. Effective barriers toincreased use include the limited availability of irrigated agricultural land near municipal centers, and thecompetition with more cost-effective, higher-value urban uses for reclaimed water.

Much of the wastewater in the United States is produced in regions where agricultural irrigation is not neededor is only occasionally needed. Judging from the acreage of irrigated cropland compared to the availability ofreclaimed wastewater and the current pattern of reclaimed water use, only a very small fraction of the food cropsin the United States would ever be exposed to reclaimed wastewater.

Treated sewage sludge is an end product of municipal wastewater treatment and contains many of thepollutants that are removed from the influent wastewater during treatment. The nutrients and organic matter intreated sludge resembles those in other organic waste-based soil amendments such as animal manure and organiccomposts. The use of sludge as a soil conditioner serves to improve soil physical properties in a manner similar toother organic-based soil amendments. While sewage sludge has been land applied since it was first produced,most of the early operations were carried out with little regard for possible adverse impacts to soil, crops, orground water. In the past two decades, more emphasis has been placed on applying treated sludges to cropland atagronomic rates.

The financial incentive for farmers to use sewage sludge in crop production is debatable. Fertilizers presentlyaccount for a relatively small percentage of total crop production costs, and sewage sludge may be more difficultto use than commercial fertilizer. However, the nutrient value of sludge is promoted as a benefit, and the POTWoften provides for transport and application of sludge for free or at a nominal cost.

Community-wide source control and industrial wastewater pretreatment programs have resulted in significantreduction of toxic pollutants in wastewater and thus in sewage sludge. Still, land application of treated effluentsand treated sludge will increase the level of toxic


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chemicals and pathogens in the soil. The public is concerned about pollutants and pathogens that may contaminatefood crops or be transported elsewhere in the environment.

If the total amount of municipal sludge produced in the United States were applied to cropland at agronomicrates, less than 2 percent of the nation's cropland would be necessary to accept it. However, there are some regionswhere limited cropland acreage may constrain sludge management options. A lack of available disposal optionsnear densely populated urban centers has forced many municipalities to seek distant disposal and land applicationsites at considerable costs. Given these economic and geographic constraints, it is not likely that all of the sewagesludge will be applied to cropland in the foreseeable future, and thus only a very small percentage of the foodcrops grown in the United States would ever be exposed to sewage sludge.

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ecosystems. J. Applied Ecol. 19:759–772.Asano, T., R. G. Smith, and G. Tchobanoglous. 1985. Municipal wastewater: treatment and reclaimed water characteristics in Irrigation with

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Bouwer, H. and E. Ideloviteh. 1987. Quality requirements for irrigation with sewage water. J. Irrig. Drainage Engineering 113:516–535.Brewer, S. R., M. Benninger-Traux, and G. W. Barrett. 1994. Mechanisms of ecosystem recovery following eleven years of nutrient

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Regulation.Harper, J. K. 1993. Production Budget. University Park: Department of Agronomy, Pennsylvania State University.Hinesly, T. D., R. L. Jones, and E. L. Ziegler. 1972. Effects on corn by application of heated anaerobically digested sludge. Compost Science

13(4):26–30.


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Hyder, M. B., and G. W. Barrett. 1986. Effects of nutrient enrichment in the producer trophic level of a sixth-year old-field community. OhioJ. Sci. 86:10–14.

Kirkham, M. B. 1974. Disposal of Sludge on Land: Effects on Soils, Plants, and Ground Water. Compost Science 15(2):6–10.Kruse, E. A., and G. W. Barrett. 1985. Effects of municipal sludge and fertilizer on heavy metal accumulation in earthworms. Environ. Pollut.

(Series A) 38:235–244.Kuchenrither, R. D., and S. Carr. 1991. A review of the National Sewage Sludge Survey Results. 62nd Annual Meeting, Water Pollution

Control Assn., Springfield, MO. Water Environment Federation, Alexandria, Vir.Kuchenrither, R.D., and S. I. McMillan. 1990. A review of the National Sewage Sludge Survey results. Biocycle, July:60–62.Levine, M. B., A. T. Hall, G. W. Barrett, and D. H. Taylor. 1989. Heavy metal concentrations during ten years of sludge treatment to an old-

field community. J. Environ. Qual. 18:411–418.Logan, T. J., and R. L. Chaney. 1983. Metals. Pp. 235–323 in Utilization of Municipal Wastewater and Sludge on Land, A. L. Page, T. L.

Gleason, J. E. Smith, I. K. Iskander, and L. E. Sommers, eds. Riverside: University of California.Logsdon. 1993. Beneficial biosolids. Biocycle (34); 2:42–44.Maly, M. S., and G. W. Barrett. 1984. Effects of two types of nutrient enrichment on the structure and function of contrasting old-field

communities. American Midland Naturalist 111:342–357.Martens, D.C., and D.T. Westermann. 1991. Fertilizer applications for correcting micronutrient deficiencies in micronutrients in agriculture.

Mortvedt, J. J., et al., eds. Soil Science Society of America Book Series No. 4. Madison, Wis.: American Society of Agronomy.McGrath, S. P., A. C. Chang, A. L. Page, and E. Witter. 1994. Land application of sewage sludge: Scientific perspectives of heavy metal

loading limits in Europe and the United States. Environ. Rev. 2:108–118.Mertz R. C. 1956. Continued study of wastewater reclamation and utilization. California State Water Pollution Control Board Publication No.

15, Sacramento: California State Water Pollution Control Board.Miller, K. J. 1990. U.S. water reuse: current status and future trends. Selected Readings on Water Reuse. EPA 430/09/91/022. Washington,

D.C.: U.S. Environmental Protection Agency.Millner, P. D. 1994. Land application of biosolids: A critical linkage between sustainable urban and agricultural systems. Pp. 12:15–19 in

Management of Water and Wastewater Solids for the 21st Century: A Global Perspective. Special Conference Series ProceedingsJuly 19–22, 1994. Alexandria Vir.: Water Environment Federation

National Academy of Sciences-National Academy of Engineering. 1973. Water Quality Control Criteria 1972: A Report of the committee onWater Quality Criteria. EPA R3/73/033. Washington, D.C.: U.S. Environmental Protection Agency.

Page, A. L., T. G. Logan, and J. A. Ryan, eds. 1987. Land Application of Sludge. Chelsea, Mich.: Lewis Publishers.


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Proceedings of the Second Conference on Environmentally Sound Agriculture. American Society of Agriculture Engineers, St.Joseph, MI.

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J. Water Pollut. Contr. Fed. 62:216–226.Snow, J. 1936. Snow on Cholera, Being a reprint of two papers by John Snow M. D. Hafner Publishing Co. LondonSolley, W. B, R. R. Pierce and H. A. Perlman. 1993. Estimated use of water in the United States in 1990. Circular 1081. Washington, D.C.:

U.S. Geological Survey.Sommers, L. E. 1977. Chemical composition of sewage sludges and analysis of their potential use as fertilizers. J. Environ. Qual. 6:225–232.Sutton, S. D., G. W. Barrett, and D. H. Taylor. 1991. Microbial metabolic activities in soils of old-field communities following eleven years of

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Yanko, W. A. 1993. Analysis of 10 years of virus monitoring data from Los Angeles County treatment plants meeting California wastewaterreclamation criteria. Water Environ. Research 65.


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3

Municipal Wastewater and Sludge Treatment

At municipal wastewater treatment plants in the United States, raw municipal wastewater undergoespreliminary, primary, secondary, and in some cases, additional treatment to yield treated effluent and aconcentrated stream of solids in liquid, called sludge. The sludge is treated as required for utilization or disposal,and additional treatment of effluent may be needed to accommodate specific water reuse opportunities.

The practice of municipal wastewater treatment evolved primarily to accommodate discharge of treatedeffluent to surface waters, not to facilitate use of effluent on crops (see Chapter 2). Because municipal wastewatertreatment techniques are well established in the United States and because effluent from some municipalwastewater treatment facilities is discharged both to surface water and used to irrigate agricultural land, secondaryor higher levels of wastewater treatment typically precede wastewater reuse in agriculture in the United States.

The relationship of municipal wastewater and sludge treatment to crop production is shown schematically inFigure 3.1. As illustrated, reuse of wastewater for food crop production or in other reuse applications, such asground water recharge or urban landscape irrigation, typically occurs after secondary wastewater treatment andmay necessitate additional treatment. Treatment to produce reclaimed water often adds coagulation, filtration, anddisinfection to secondary treatment. Figure 3.1 also illustrates the origin and treatment of municipal wastewatersludges applied to cropland. Following treatment, sludges may be disposed of (for example, in a landfill) or usedfor food crop production or in other applications (such as silviculture and nonfood crop agriculture).

This chapter briefly reviews typical amounts and properties of treated effluent and sludge, then examinesprocesses used in conventional wastewater treatment (defined as preliminary, primary, and secondary treatment),processes intended specifically to accommodate wastewater application to crops, and typical sludge treatmentprocesses.

QUANTITY AND QUALITY OF MUNICIPAL WASTEWATER EFFLUENT AND SLUDGE

Municipal wastewater represents the spent water supply of communities. In 1990, average

MUNICIPAL WASTEWATER AND SLUDGE TREATMENT 45

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FIGURE 3.1 Following conventional wastewater treatment (preliminary, primary, and secondary), municipalwastewater is discharged to surface waters or reused, or before discharge to surface waters (not illustrated).Additional treatment may be needed before reuse. Sludge from wastewater treatment processes are treated and thendisposed or reused in crop production or other applications.

per capita usage from public water supply systems in the United States was 184 gallons (700 liters) per day(Solley et al., 1993). In arid areas, municipal wastewater production is typically less than the amount withdrawnfor water supply, but in some areas, wastewater flow exceeds the water supply because of infiltration and inflow(e.g. stormwater) into wastewater collection systems. Using 85 percent of water use as an estimate of typicalwastewater production (Henry and Heinke, 1989), a city of 200,000 people would produce an average of about31,000,000 gal/day (about 117,000 m3/day) of raw wastewater. The amount of treated wastewater effluentextracted is not appreciably diminished from the original quantity of raw wastewater particularly if sludge isdewatered, as is common.

The quality of treated effluent from secondary wastewater treatment plants in the United


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States must comply with the federal regulation of a monthly average of 30 milligrams per liter of biochemicaloxygen demand or BOD (a measure of the amount of biodegradable organic material remaining in the treatedwastewater) and 30 mg/liter of suspended solids (particles removable by filtration). Typical concentrations ofother constituents in wastewater treatment plant effluent are summarized in Chapter 2 . More detailed informationon typical effluent quality is presented in sections of this report where potential effects of individual constituentsare considered. For example, Chapter 5 includes information on the types and quantities of pathogens typicallyfound in various wastewater treatment plant effluents.

The volume of municipal wastewater sludge produced by wastewater treatment facilities is an elusivequantity because it varies as a result of typical sludge treatment (see ''Volume Reduction Processes" later in thischapter). Since the mass of dry solids is conserved during most treatment processes, dry weight is a more usefulbasis for expressing the amount of sludge from municipal wastewater treatment. Typical primary and secondarywastewater treatment produces a total of about 1.95 lbs (0.94 kg) of dry solids per 1,000 gal (3.78 m3) ofwastewater treated (Metcalf and Eddy, 1991). Chemical addition to sludges during conditioning and stabilizationprocesses (see later sections of this chapter) can appreciably increase the mass of solids in sludges. Biologicalstabilization acts to reduce the mass of suspended solids through oxidation of some of the volatile organic solids insludges. For example, if sludge contains 80 percent volatile suspended solids and 50 percent of them are destroyedthrough oxidation, the stabilized mass of sludge solids would be reduced to 60 percent of the initial mass.

Typical solids contents of sludges at various stages of treatment are summarized in this chapter. Typicalranges of other common constituents in sludges are summarized in Chapter 2. As with wastewater effluents, moredetailed information about specific sludge constituents is found in sections of the report where the potential effectsof those constituents are discussed.

CONVENTIONAL WASTEWATER TREATMENT PROCESSES

Municipal wastewater treatment typically comprises preliminary treatment, primary treatment, and secondarytreatment. Secondary treatment is the United States national standard for effluent discharged to surface waters. Ahigher degree of treatment, termed here "advanced" or "tertiary" treatment, may be required at specific locations toprotect health or environmental quality. In this report, conventional municipal wastewater treatment is consideredto include screening, grit removal, primary sedimentation, and biological treatment because it is the most commonmethod (Figure 3.2). Elaboration on these terse descriptions may be found in sources such as Henry and Heinke(1989) and Metcalf and Eddy (1991).

Preliminary Wastewater Treatment

Preliminary wastewater treatment ordinarily includes screening and grit removal. Wastewater screeningremoves coarse solids such as rags that would interfere with mechanical equipment. Grit removal separates heavy,inorganic, sandlike solids that would settle in channels and interfere with treatment processes.


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FIGURE 3.2 Municipal wastewater is conventionally subjected to preliminary, primary, and secondary treatment inthe United States. Additional tertiary or advanced treatment may be justified by local conditions. Processes typicallyinvolved in each stage of treatment are shown. Preliminary treatment effects minimal change in wastewater quality.Primary treatment typically removes about one-third of the BOD and one-half of the suspended solids in domesticwastewaters. Combined primary and secondary treatment is required to achieve 85 percent reduction in both BODand suspended solids concentration to meet the regulatory definition of secondary treatment.

Preliminary treatment serves to prepare wastewater for subsequent treatment, but it effects little change inwastewater quality. The residues from preliminary wastewater treatment, screenings and grit, are not ordinarilyincorporated with sludges, and they are not considered further in this report.

Primary Wastewater Treatment

Primary wastewater treatment usually involves gravity sedimentation of screened, degritted wastewater toremove settleable solids; slightly more than one-half of the suspended solids ordinarily are removed. BOD in theform of solids removable by sedimentation (typically about one-third of total BOD) is also removed. At one timeduring the evolution of domestic wastewater treatment in the United States, facilities only practiced primarywastewater treatment and the primary effluent was commonly discharged to surface waters offering appreciabledilution. Now, primary treatment is used as an economical means for removing some contaminants prior tosecondary treatment. The residue from primary treatment is a concentrated suspension of particles in water called"primary sludge."

Although the goal of primary wastewater treatment is to separate readily-removable suspended solids andBOD, wastewater constituents that exist as settleable solids or are sorbed to settleable wastewater solids may alsobe removed. Thus, primary treatment effects some reduction in the effluent concentration of nutrients, pathogenicorganisms, trace elements, and potentially toxic organic compounds. The constituents that are removed arecontained in primary sludge.


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Secondary Wastewater Treatment

Secondary municipal wastewater treatment is almost always accomplished by using a biological treatmentprocess. Microorganisms in suspension (in the "activated sludge" process), attached to media (in a "trickling filter"or one of its variations), or in ponds or other processes are used to remove biodegradable organic material. Part ofthe organic material is oxidized by the microorganisms to produce carbon dioxide and other end products, and theremainder provides the energy and materials needed to support the microorganism community. Themicroorganisms biologically flocculate to form settleable particles, and, following biological treatment, this excessbiomass is separated in sedimentation tanks as a concentrated suspension called "secondary sludge" (also knownas "biological sludge,'' "waste activated sludge," or "trickling filter humus").

Wastewater constituents can become associated with secondary sludge as a result of microbial assimilation,by sorption onto settleable solids, or by incorporation into agglomerate particles formed as a result ofbioflocculation. Some of the wastewater constituents that are incidentally associated with the biomass fromsecondary treatment processes include pathogens, trace elements, and organic compounds.

Tertiary or Advanced Wastewater Treatment

Tertiary treatment is used at municipal wastewater treatment plants when receiving water conditions or otheruses require higher quality effluent than that produced by secondary wastewater treatment. Disinfection forcontrol of pathogenic microorganisms and viruses is the most common type of tertiary treatment. Theconcentrations of suspended solids and associated BOD in treated effluent can be reduced by filtration, sometimeswith the aid of a coagulant. Adsorption, ordinarily on activated carbon, can be used to remove some persistentorganic compounds and trace elements. The concentration of ammonia in secondary effluent can be reduced bynitrification. Tertiary treatment to remove nitrogen and phosphorus, so as to minimize nutrient enrichment ofsurface waters, is common; nitrogen is usually removed by nitrification followed by denitrification, andphosphorus is removed by microbial uptake or chemical precipitation. Not all tertiary treatment processes followsecondary treatment, as was shown schematically in Figure 3.1; nutrient removal, for example, can be achieved bydesign and operational variations to primary and secondary treatment processes. The residues from tertiarytreatment typically become incorporated with sludges from primary and secondary treatment.

There are many variations to these treatment practices. For instance, secondary treatment is rarely achievedusing physical and chemical processes rather than biological treatment. Primary treatment is sometimeseliminated. Long-term retention in lagoons is sometimes substituted for both primary and secondary treatment.


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TREATMENT TO FACILITATE CROP IRRIGATION WITH RECLAIMED WATER

The degree of wastewater treatment required prior to using wastewater effluent for crop production dependson the crop, local conditions, and state regulations. In considering specific applications of reclaimed wastewaterfor crop production, tradeoffs may exist between degree of wastewater treatment needed and agriculturalpractices.

Special treatment to allow agricultural use of treated effluents is not always considered necessary by statesthat regulate the practice (see Chapter 7); effluents from conventional primary and secondary wastewatertreatment are used. Indeed, historically, untreated raw wastewater has been used, but the practice is not found inthe United States and is not considered herein.

In identifying appropriate wastewater treatment for crop application, it is appropriate to consider protectionof health and environmental quality, water quality requirements of crops, and requirements of the irrigation waterstorage and delivery system (such as avoiding odors and clogging) (EPA, 1981; Water Pollution ControlFederation, 1983). As a practical matter, the extent of wastewater treatment required prior to food crop applicationordinarily is established by health and environmental quality considerations. Disinfection and suspended solidsremoval are the processes most frequently used to further improve conventional wastewater treatment planteffluents for use on crops.

Disinfection of treated effluent is most often accomplished by chlorination. Chlorine is an economicaldisinfectant, but it reacts with organic material in wastewater effluent to form chlorinated organic compounds thatare of potential concern with potable reuse of reclaimed wastewater, but not with irrigation (see Chapter 6).Alternatives to chlorine as a wastewater disinfecting agent include ozone and ultraviolet light. The latter twoprocesses do not provide a residual disinfectant as required by some state regulations for applying treatedwastewater to food crops (EPA, 1992).

Additionally, suspended solids are sometimes removed from conventional wastewater treatment planteffluent prior to using the effluent in agriculture. Removal of suspended solids aids in control of pathogenicorganisms and viruses by making disinfection more effective. Suspended solid removal minimizes deposition ofsolids on top of soils, and reduces clogging of some irrigation water delivery systems. Further reduction ofsuspended solids in effluent is typically achieved by adding a coagulating chemical, settling, and filtering throughgranular media (Faller and Ryder, 1991; Kuo, et al., 1994).

Treatment technology to produce any degree of wastewater quality perceived to be necessary for food cropproduction is available; however, treatment costs escalate with incremental water quality improvements.Additionally, residue (sludge) management problems accompany some processes (such as those usingmembranes) that might be used to improve treated wastewater quality beyond the current norms. Situations existtoday in which water quality discharge requirements, the crop value and water scarcity justify the higher degreesof wastewater treatment before application to food crops.


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SLUDGE TREATMENT PROCESSES

Primary and secondary sludges may be expected to contain settleable materials from raw wastewater and theproducts of microbial synthesis. Other materials are also removed from wastewaters and incorporated into primaryand secondary sludges, however. The large surface area of particles incorporated into sludges provides sites foradsorption of constituents from the liquid phase. Nondegraded organic compounds in solution may partition intothe organic fraction of the particles. Bioflocculation may incorporate colloidal particles that otherwise would notbe removed by sedimentation into settleable particles. These and other mechanisms result in selective enrichmentof wastewater constituents in sludge. Additionally, wastewater sludges are mostly water and, hence, wastewaterconstituents remaining in the liquid phase also are included in sludges.

Because primary and secondary sludges have different properties, advantage is sometimes sought by treatingthem separately. As an illustration, secondary sludge thickens better using the dissolved air flotation process (seefollowing section) than by gravity thickening, and it is sometimes thickened separately from primary sludge. Thetwo sludges almost invariably are combined prior to the end of the treatment, and, for purposes of discussing theultimate utilization of treated sludge, they are not further distinguished.

A wide variety of sludge treatment processes are used to reduce sludge volume and alter sludge propertiesprior to disposal or use of the treated product. The nature of these processes is summarized in the sections thatfollow. Additional details may be found in sources such as Dick (1972), Vesilind (1979), and EPA (1977), andMetcalf and Eddy (1991).

Sludge treatment is considered herein to comprise engineered processes for altering sludge quality prior todisposal or reclamation. When sludge is applied to land, inactivation of remaining pathogenic organisms andviruses continues, biological stabilization of residual organic material progresses, and biologically-mediated andabiotic chemical transformations occur.

Volume Reduction Processes

Biological sludge, as produced from secondary wastewater treatment processes, often has a suspended solidscontent of less than one percent by weight; that is, each kg of activated sludge solids is accompanied by more than99 kg of water. Primary sludges are more concentrated, but marginally so; typical combined primary andsecondary sludge might contain about 3 percent solids by weight. Because of the voluminous nature of sludges,processes categorized here as "thickening," "dewatering," "conditioning,'' and "drying" (listed in order ofdecreasing frequency of application) are common in sludge management. Removal of water from sludgesimproves efficiency of subsequent treatment processes, reduces storage volume, and decreases transportationcosts.

Thickening

Sludge thickening produces a concentrated product that essentially retains the properties


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of a liquid. Gravity thickening, or concentration by simple sedimentation, is the thickening process mostcommonly applied to municipal sludges. The product of gravity sludge thickening often contains 5 to 6 percentsolid material by weight. Alternatives to gravity thickening include flotation thickening (in which a gas isincorporated with sludge solids, causing them to float), as well as the use of gravity drainage belts, perforatedrotating drums, and centrifuges.

Dewatering

Sludge dewatering processes produce material with the properties of a solid, even though the dewateredsludge is still mostly water. Dewatered sludge can be transported in a dump truck, whereas a tank truck is requiredto transport thickened sludge. Dewatering may be accomplished on sand drying beds and, occasionally, inlagoons, where gravity drainage and evaporation removes moisture. More often, larger municipal installations usemechanical means for dewatering sludge. Mechanical sludge dewatering equipment includes filter presses, beltfilter presses, vacuum filters, and centrifuges. The solids content of mechanically dewatered sludge typicallyranges from 20 to 45 percent solids by weight; most processes produce concentrations of solids at the lower end ofthat range.

Conditioning

Sludge conditioning processes do not, in and of themselves, reduce the water content of sludge. Conditioningalters the physical properties of sludge solids to facilitate the release of water in dewatering processes. Indeed, themechanical dewatering techniques discussed in the previous paragraph would not be economical without priorsludge conditioning. Chemical and, less frequently, physical techniques are used to condition sludge. Chemicalconditioning most commonly involves adding synthetic organic polyelectrolytes (or "polymers") to sludge prior todewatering. Inorganic chemicals (most commonly, ferric chloride and lime in the United States) can also be used.Inorganic chemical conditioning dosages are large, and increase the mass of the solid phase of sludge. Physicalconditioning techniques include heat treatment and freezethaw treatment.

Drying

If circumstances justify removal of water beyond that achievable by dewatering processes, drying is needed.Thermal drying with direct or indirect dryers is used to achieve near-complete removal of water from sludges.Solar drying is feasible in some locations. Partial drying also results from heat produced in biochemical reactionsduring composting and from other chemical reactions described in the stabilization processes below.


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Stabilization Processes

The purpose of sludge stabilization is to minimize subsequent complications due to biodegradation of organiccompounds. Stabilization is usually accomplished by biological or chemical treatment processes, as describedbelow.

The vector attraction reduction provisions of the Part 503 Sludge Rule (EPA, 1993a) concern stabilizationprocesses. Vectors, such as flies, are organisms that might be attracted to unstabilized sludge and are capable oftransmitting infectious diseases. Stabilization process performance requirements are specified in the Part 503Sludge Rule for both biological and chemical stabilization. When sewage sludge is applied to agricultural land,vector attraction reduction requirements can also be satisfied by injecting sludge below the surface orincorporating sludge into the soil.

Stabilization can also be achieved by drying sludge adequately to impede microbial activity. Obviously,sludge combustion, too, accomplishes the stabilization objective. Many stabilization processes can also causeappreciable inactivation of pathogenic organisms and viruses. Inactivation of pathogens in sludges is consideredseparately in a subsequent section.

Biological Stabilization

In biological stabilization processes, the organic content of sludges is reduced by biological degradation incontrolled, engineered processes. Most commonly, domestic wastewater sludge is biologically stabilized as aliquid in anaerobic digesters from which methane gas is a byproduct. Liquid sludge can also be biologicallystabilized in aerobic digesters to which oxygen (or air) must be added. Composting is a process that biologicallystabilizes dewatered sludge. Composting is ordinarily an aerobic process, and an amendment such as wood chipsor sawdust must be added to improve friability in order to promote aeration. Composting takes place atthermophilic temperatures (often, about 55¹C) because of heat released by biochemical transformations. Aerobicdigesters can be made to operate thermophilically using heat from the same source. Anaerobic digesters canoperate at thermophilic temperatures by burning methane produced from the process, but they typically operate atmesophilic temperatures (at about 35¹C) in the United States.

Chemical Stabilization

Chemical stabilization of sludges is aimed not at reducing the quantity of biodegradable organic matter, butat creating conditions that inhibit microorganisms in order to retard the degradation of organic materials andprevent odors. The most common chemical stabilization procedure is to raise the pH of sludge using lime or otheralkaline material, such as cement kiln dust. Sludge can be chemically stabilized in liquid or dewatered forms.When dewatered sludge is used, the exothermic reaction of lime with water causes heating which helps destroypathogens and evaporate water.


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Inactivation of Pathogenic Organisms and Viruses

Many of the processes for drying and stabilizing sludges can be designed and operated to achieve appreciableinactivation of pathogenic agents, including bacteria, parasites, and viruses. Alternatively, sludge treatmentprocesses specifically intended to control pathogenic organisms and viruses can be used. Processes specificallyintended for inactivating pathogens include irradiation and pasteurization; these processes currently are not widelyused in the United States.

In the Part 503 Sludge Rule, (EPA, 1993a) the pathogenic quality of sludge is controlled by categorization ofsludges as either "Class A" (safe for direct contact) or "Class B" (crop and site restrictions required), according tocriteria for the destiny of indicator and pathogenic organisms and by specification of process performance. ThePart 503 Sludge Rule identifies specific processes with regard to their capability for pathogen destruction.Processes that can be used to reach the Class B category are identified by EPA as "Processes to SignificantlyReduce Pathogens." These including aerobic digestion, air drying, anaerobic digestion, composting, and limestabilization, or any combination of processes that can reduce fecal coliform less than 2,000,000 colony formingunits per gram of total dry solids. EPA identifies more effective processes that can be used to reach the Class Acategory called "Processes to Further Reduce Pathogens." These Class A processes include composting at higher,controlled temperatures, heat drying, heat treatment, thermophilic aerobic digestion, beta ray irradiation, gammaray irradiation, and pasteurization as well as high-level alkaline treatment and other processes that can bedemonstrated to reduce pathogens to below detectable levels. Human health concerns about pathogenic organismsand viruses in sludge are considered in more detail in Chapter 5, and regulations to control infectious diseasetransmission from the use of sludge in crop production are discussed in Chapter 7.

Other Sludge Treatment Processes

A wide variety of processes are used to treat sludges. Those briefly discussed in this section ordinarily areless relevant to sludge management schemes directed towards food crop production than are the processespreviously discussed.

Solidification/Immobilization

Solidification/immobilization processes involve the conversion of sludge to a solid material with load-bearingcapacity and the incorporation of contaminants in the solid phase so as to minimize their migration. Thetechnology for solidifying and immobilizing waste originated in the nuclear waste industry, and although it hasbeen widely applied in attempts to control hazardous waste, it is less commonly applied to municipal sludges.


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Metal Stripping and Toxic Organic Destruction

Research has been conducted on selective removal of trace metals from municipal sludges and destruction oftoxic organic compounds in sludges. These processes are not commonly used and were not considered in thisreport. Control of trace elements and toxic organic compounds in sludges is more appropriately managed by theregulation of wastewater at its sources.

Combustion

Combustion destroys organic compounds in municipal sludges and leaves an inorganic dry ash. Rarely,sludge combustion is carried out in the liquid phase under high pressure, producing an ash in liquid suspension.

Because most of the organic material in sludge has beneficial attributes in agricultural systems, thecombustion process is inappropriate when sludges are to be applied to cropland. Accordingly, combustion is notconsidered further in this report.

Ultimate Sludge Utilization or Disposal

Options for ultimate use or disposal of municipal wastewater sludges are quite restricted. The Clean WaterAct and the Ocean Dumping Ban Act eliminated all but land-based options for ultimate use or disposal ofmunicipal wastewater treatment sludges. Any attempt to extract and recycle materials from sludges is unrealisticdue to the highly heterogeneous nature of municipal wastewater sludge. With the exception of sludge ash used inbuilding materials, municipal wastewater sludges currently are land-applied for beneficial uses or disposed of onthe land.

Beneficial uses of treated municipal wastewater sludges on land include agriculture and silviculture uses;application to parks, golf courses, and public lands; use in reclaiming low quality or spoiled lands; and use aslandfill cover or fill material. Disposal on land includes landfilling and permanent storage of dewatered sludge orsludge incinerator ash in lagoons or piles.

Integrated Sludge Management Schemes

The large number of alternatives for accomplishing of the many objectives of sludge treatment lead to manyvariations in municipal sludge management schemes. When sludge is applied to agricultural land, the extent ofwater removal during its treatment is a major factor influencing cost and process selection. It is not necessary toremove water from sludge prior to land application—indeed, the water may be beneficial to crops. Sludgedewatering is justified when its cost is offset by savings in transportation costs. Optimization of sludge treatmentprocess integration by Dick, et al. (1982) illustrated that lengthy transport may be cheaper than sludge dewatering.Sludge drying, which is more expensive than sludge dewatering, allows further reduction in transport costs, andalso enables sludge to be stored and packaged.


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Figures 3.3a, b, and c illustrate sludge management schemes for agricultural application of liquid, dewatered,and dried municipal sludges, respectively. Liquid sludge discharge to agricultural land, as illustrated in Figure 3.3a,is the simplest scheme, but substantial liquid storage capacity might be needed if land application sites areunavailable for extended periods. Agricultural application of dewatered sludge, as illustrated in Figure 3.3b,requires more expensive and extensive processing, but could be compatible with other disposal and use optionsthat may be used in addition to agricultural use. Inclusion of drying in the sludge process-flow as diagramed inFigure 3.3c is ordinarily the most costly of the three options. Storage to accommodate agricultural demand iseasiest when sludge is dried, and dried sludge can also be adapted to other disposal and use options.

Integration of sludge treatment processes for use on agricultural land also requires consideration of the effectsof the treatment processes on sludge quality. For example, dewatering, composting, or alkaline treatment can beexpected to reduce the amount of nitrogen in sludge that is available to plants. This would require on increase inthe areal rate of sludge solids applied to satisfy the plant nitrogen demand, and would, in turn, increase the rate atwhich trace metals and toxic organic chemicals associated with the sludge solids were applied to soil.

INDUSTRIAL WASTEWATER PRETREATMENT

Pretreatment of industrial wastewaters is a means to manage toxic contaminants in treated wastewatereffluents and sludge residuals. It is defined as "the removal of toxic materials as the industrial plant before thewastewater is released to the municipal sewer" (National Research Council, 1977). Because industrial activity is asubstantial source of toxic chemicals in sludge and reclaimed wastewater in populated metropolitan areas,pretreatment programs have been effective in reducing the concentrations of most heavy metals in wastewater(refer back to Tables 2.3, 2.4, 2.5, and 2.6). They are grouped in four Priority Pollutant categories: Section 307 ofthe Clean Water Act regulates 127 hazardous compounds, (1) 14 heavy metals and cyanide, (2) 28 volatile organiccompounds, (3) 58 semi-volatile organic compounds and (4) 25 pesticides and polychlorinated biphenyls (PCBs)(40 CFR 123.21 (1986)).

Fate of Toxic Chemicals During Secondary Wastewater Treatment

As will be discussed below, most of the priority pollutants in wastewater accumulate in sludge during thewastewater treatment process (Lue-Hing et al., 1992).

Heavy Metals

Investigations of heavy metal partitioning in secondary wastewater treatment plants include both surveys ofoperating POTWs (Mytelka et al., 1973; Oliver and Cosgrove, 1974; EPA, 1982) and more controlled pilot-plantstudies (Petrasek and Kugelman, 1983; Patterson and Kodukula, 1984; Hannah et al., 1986). Researchers havefocused on seven heavy metals:


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FIG

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cadmium, chromium, copper, lead, mercury, nickel, and zinc. These heavy metals are partitioned ontosludges both in primary wastewater treatment such as sedimentation, and in biological secondary treatmentprocesses such as like activated sludge. From 5 to 50 percent of these metals were found to have been removedfrom wastewater and concentrated into primary sludge. Removal of heavy metals in secondary biological sludgeswas greater: 15 to 80 percent. Combining the findings of a number of studies (Lue-Hing et al., 1992; Cheng et al.,1975; Neufield et al., 1975), the removal of heavy metals from wastewater into secondary sludge is reported to be(in declining order): mercury, copper, lead, chromium, cadmium, zinc, and nickel.

Cyanide

In a study of 40 selected POTWs, removal of cyanide from untreated sewage was found to vary between 7and 98 percent (Lue-Hing, et al., 1992). This wide removal range is somewhat deceptive. The minimum removalwas associated with a very low influent cyanide concentration, 0.003 mg/liter. The maximum reported influentwastewater concentration, 7.58 mg/liter, was associated with higher removals. Many researchers have verified thatcyanide is relatively biodegradable by aerobic (Knowles and Bunch, 1986) and anaerobic (Fallon, 1992) metabolicpathways. Richards and Shieh (1989) found that cyanide was removed from wastewater by activated sludge inconcentrations of up to 100 mg/liter. It is likely then that small amounts of cyanide from industrial discharge intosewers are destroyed during secondary treatment and are not concentrated into sludge (Lordi et al., 1980).

Toxic Organic Chemicals: Volatile and Semivolatile Organic Compounds, Pesticides and PCBs

There are 111 organic priority pollutants, which constitute the majority percent of the hazardous chemicalsregulated in wastewater. Unlike heavy metals, which are concentrated in sludge, many organic priority pollutantsare removed from wastewater by a variety of mechanisms: volatilization during secondary treatment aeration,sedimentation and sorption onto both primary and secondary sludges, and biodegradation (Hannah et al., 1986;Petrasek et al., 1983; Kincannon et al., 1983; Tabak et al., 1981). Seven of the organic priority pollutants werefound in over 50 percent of samples of treated wastewater effluent from 40 POTWs in the United States: 1,1,1-trichloroethane (52 percent), chloroform (82 percent), methylene chloride (86 percent), bis (2-ethylhexyl)phthalate (84 percent) and di-n-butyl phthalate (52 percent) (EPA, 1982).

Hannah et al. (1986) and Petrasek et al. (1983) conducted activated sludge pilot-plant studies on 21 and 22organic priority pollutants, respectively. Reported removals ranged from 18 to 99 percent; the investigators foundthat over 90 percent of the majority of the organic chemicals were removed by the activated sludge process.Volatile organic priority pollutants were not concentrated into either primary or secondary sludge; however,semivolatile organic priority pollutants did accumulate in primary and secondary sludges, with concentrationfactors


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ranging from 5 to 200. High concentration factors were associated with higher molecular weight polyaromatichydrocarbons and phthalate compounds.

Pretreatment

As discussed above, toxic heavy metals and those organic priority pollutants which are not biodegraded orvolatilized are concentrated in wastewater sludge. The National Research Council (1977) reported thatpretreatment has the potential to alleviate problems of sludge disposal due to heavy metals and toxic organiccompounds. In a study of operating POTWs in Chicago, Illinois and in a pilot study at a POTW in Buffalo, NewYork where significant amounts of industrial wastewater discharge were received, it was found that industrialpretreatment programs reduced toxic heavy metal concentrations by a range of 50 to over 90 percent (Zenz, et al.,1975; EPA, 1977).

Pretreatment Goals

The General Pretreatment Regulations of the Clean Water Act (40 CFR 403 (1978)) establishes limits onindustrial discharges of hazardous pollutants to municipal sewers in order to:

• prevent the introduction of pollutants which will interfere with the performance of the POTW treatmentprocesses for wastewater and sludge;

• prevent the pass-through of toxic pollutants into surface waters receiving discharges of treated wastewatereffluent; and

• enhance opportunities to recycle treated municipal wastewater and sludge (EPA, 1993b)•

Pretreatment Implementation

The pretreatment regulations identify strategies for setting numerical standards on industrial dischargers toPOTWs. First, 34 categories of industries have been identified as potential sources of priority pollutants inwastewater, and standards have been set for 29 of these categorical dischargers based on the best availabletechnology. Second, discharge standards that prohibit hazardous pollutants enable POTWs to increase the scope oftheir pretreatment regulation to include all nondomestic users of municipal sewers, in addition to the categoricaldischargers. Finally, the local POTW can set more stringent limits based on its specific requirements, and thesealso are federally enforceable. (Lue-Hing et al., 1992; Outwater, 1994).

More recently, the third goal of pretreatment, to enhance POTWs' ability to beneficially use sludge andreclaim wastewater, has been added to the regulation of industrial wastewater. Because heavy metals and manytoxic organic chemicals accumulate in sludge, it is necessary to control not only the end-of-the-pipe concentrationof hazardous compounds with standards,


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but to limit the total mass loading of pollutants that are concentrated in sludge (Outwater, 1994). For example, ithas been reported that protection of sludge quality has caused a POTW in Georgia to set heavy metal dischargelevels two orders of magnitude below categorical pretreatment limits for these compounds (Ford et al., 1994).

SUMMARY

Conventional municipal wastewater treatment processes were developed to produce effluents suitable fordischarge to surface waters. The processes are intended primarily to remove BOD and suspended solids, butwastewater constituents associated with particles are also removed. Thus, substantial removal of tracecontaminants may occur in conventional treatment even though the treatment processes were not designed fortrace metal or toxic chemical removal.

When required by receiving water conditions or effluent reuse practices, advanced, or tertiary, wastewatertreatment processes may be used in addition to conventional municipal wastewater treatment processes.Destruction of pathogenic organisms and increased removal of suspended solids or nutrients are some of the goalsof tertiary treatment.

With the exception of compounds biologically degraded or volatilized during wastewater treatment,substances removed from wastewaters are contained in the residues, or sludges, produced. A wide variety ofsludge treatment processes are used to prepare municipal wastewater treatment sludges for use or disposal. Theobjectives of most municipal sludge treatment processes are to reduce the water content of sludges, to avoidcomplications from decomposition of the biologically degradable fraction of sludges, and to reduce the levels ofpathogenic organisms in sludges.

Economically viable technology for selective removal of trace elements and toxic organic compounds fromsludges does not exist. Amounts of these constituents in municipal sludges can currently be controlled only byregulating the quality of wastewater entering municipal waste-water collection systems. Industrial wastewaterpretreatment programs have been demonstrated to substantially improve the quality of sludge from municipalwastewater treatment. Modification of industrial processes, control of corrosivity of water in water supplysystems, and changes in the formulation of disposable consumer products are other measures needed to controlwastewater and, hence, sludge quality.

REFERENCES

Cheng, M. H., J. W. Patterson, and R. A. Minor. 1975. Heavy metals uptake by activated sludge. Jour. WPCF 47:363–376.Dick, R. I. 1972. Pp. 533–596 in Sludge Treatment, Physicochemical Processes for Water Quality Control, W. J. Weber, Jr., ed. New York:

John Wiley and Sons.Dick, R. I., D. L. Simmons, and Y. Hasit. 1982. Process Integration in Sludge Management. Water Sci. Technol. 14:765–779.


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EPA. 1977. Industrial waste and pre-treatment in the Buffalo municipal system, ORD, EPA 606/2-77-018. Ada, Okla.: U.S. EnvironmentalProtection Agency. Robert S. Kerr Environmental Research Laboratory

———. 1981. Process Design Manual for Land Treatment of Municipal Wastewater. EPA 625/1-81-013. Cincinnati, Ohio: U. S.Environmental Protection Agency.

———. 1982. Effluent Guidelines Division, Fate of Priority Pollutants in Publicly Owned Treatment Works - Final Report. Vol. 1. EPA440/1–82/303. Washington, DC.: U.S. Environmental Protection Agency.

———. 1992. Guidelines for Water Reuse. EPA 625/R-92/004. Washington D.C.: U. S. Environmental Protection Agency.———. 1993a. Standards for the Use or Disposal of Sewage Sludge; Final Rules, 40 CFR Parts 257, 403, and 503. Federal Register, 58

(32):9248–9415.———. 1993b. Pretreatment and Municipal Pollution Prevention. Washington, D.C.: U.S. Environmental Protection Agency Office of

Wastewater Enforcement and Compliance.Faller, J. A., and R. A. Ryder. 1991. Clarification and filtration to meet low turbidity reclaimed water standards. Water Environ. Technol. 3

(1):68–74.Fallon, R. D. 1992. Evidence for hydrolytic route for anaerobic cyanide degradation. Applied Environ. Microbiol. 58:3163–3163.Ford, L. J. Johnson, and M. J. DelConte. 1994. Indirect requirements for indirect dischargers. Water Environ. Technol. 6(1):59–63.Hannah, S. A., B. M. Austern, A. E. Eralp, R. H. Wise. 1986. Comparative removal of toxic pollutants by six wastewater treatment processes.

Jour. WPCF 58:27–34.Henry, J. G., and G. W. Heinke. 1989. Environmental Science and Engineering. Englewood Cliffs, N.J.: Prentice-Hall. 728 pp.Kuo, J.-F., L. Chen, J. F. Stahl, and R. W. Horvath. 1994. Evaluation of four different tertiary filtration plants for turbidity control. Water

Environment Research 66:879–886.Kincannon, D. F., E. L. Stover, V. Nichols, D. Medley. 1983. Removal mechanisms for toxic priority pollutants. Jour. WPCF 55:157–163.Knowles, C. J. and A. W. Bunch. 1986. Microbial cyanide metabolism. Adv. Microbial Physiol. 27:73–111.Lordi, D. T., C. Lue-Hing, S. W. Whitebloom, N. Kelada, S. Dennison. 1980. Cyanide problems in municipal wastewater treatment plants.

Jour. WPCF 52:597–609.Lue-Hing, C., D. R. Zenz, and R. Kuchenrither. 1992. Municipal Sewage Sludge Management. Processing, Utilization and Disposal. Water

Quality Management Library. Vol. 4. Lancaster, Pa.: Technomic Publishing.Metcalf and Eddy, Incorporated. 1991. Wastewater Engineering: Treatment Disposal and Reuse. New York: McGraw-Hill.Mytelka, A. I., J. S. Czachor, W. B. Guggino,and H. Golub. 1973. Heavy metals in wastewater and treatment plant effluents. Jour. WPCF

45:1859–1864.National Research Council. 1977. Multimedium Management of Municipal Sludge. Washington, D.C.: National Academy Press.Neufield, R. D. and E. R. Herman. 1975. Heavy metals removal by acclimated activated sludge, Jour. WPCF 47:310–329.


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Oliver, B. G., and E. G. Cosgrove. 1974. The efficiency of heavy metal removals by a conventional activated sludge treatment plant. WaterResearch 8:869–874.

Outwater, A. B. 1994. Reuse of Sludge and Minor Wastewater Residuals. Boca Raton, Fla.: Lewis Publishing.Patterson, J. W., and P. S. Kodukula. 1984. Metals distribution in activated sludge systems. Jour. WPCF 56:432–441.Petrasek, A. C., and I. J. Kugelman. 1983. Metals removals and partitioning in conventional wastewater treatment plants. Jour. WPCF

55:1183–1190.Petrasek, A. C., I. J. Kugelman, B. M. Austern, T. A. Pressley, L. A. Winslow, and R. H. Wise. 1983. Fate of organic compounds in

wastewater treatment plants. Jour. WPCF 55:1286–1296.Richards, D. J., and W. K. Shieh. 1989. Anoxic-oxic activated sludge treatment of cyanide and phenols. Biotechnol. Bioeng. 33:32.Solley, W. B., R. R. Pierce, and H. A. Perlman. 1993. Estimated use of water in the United States in 1990. U. S. Geological Survey Circular

1081. Washington, D.C.: U.S. Geological Survey. 76 pp.Tabak, H. H., S. A. Quave, C. I. Mashni, and E. F. Barth. 1981. Biodegradability studies with organic priority pollutant compounds. Jour.

WPCF, 53:1503–1518.Vesilind, P. A. 1979. Treatment and Disposal of Wastewater Sludges. Ann Arbor, Mich.: Ann Arbor Science Publishers.Water Pollution Control Federation. 1983. Water Reuse, Manual of Practice SM-3. Alexandria, Va.: Water Environment Federation.Zenz, D. R., B. T. Lyman, C. Lue-Hing, R. R. Rimkus, and T. D. Hinesly. 1975. Guidelines on sludge utilization and disposal—a review of its

impact upon municipal wastewater treatment agencies. 48th Annual Water Pollution Control Federal Conference, Miami Beach, Fla.Alexandria, Va.: Water Environment Federation.


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4

Soil, Crop, and Ground Water Effects

Using treated municipal wastewater effluents and sludge on agricultural land provides an alternative todisposal by utilizing the recyclable constituents in sludge and wastewater in the production of crops. Sewagesludge and wastewater effluents can provide essential plant nutrients and water. Sludge is also rich in organicmatter, which, if added in sufficient quantities, will improve the physical condition of the soil and render it a morefavorable environment to manage the nutrients and water. However, unlike manufactured fertilizers, whosenutrient properties can be formulated to suit the crop requirements, plant nutrients in sludges and effluents areuncontrolled. For this reason, applying treated sludges and effluents at agronomic rates to satisfy the requirementfor one nutrient may cause the levels of other nutrients to be excessive or remain deficient.

Certain source constituents in municipal wastewater and sludge (e.g, salts, cadmium, copper, nickel, andzinc) could be phytotoxic if added to the soil in excess of critical levels. Trace elements and trace organics insludge are of concern if they are taken up by crops in amounts harmful to consumers or through other pathways(see Chapter 6). The fate and transport of potentially harmful constituents in the environment are also of concern.If the constituents from sludge and effluent application are not immobilized in the surface soil, they may escapethe root zone and leach to ground water. This chapter evaluates the possible effects of the agricultural use oftreated sludge and effluent on soils, crops, and ground water resources, and includes a brief discussion oflandscape-level perspectives.

SLUDGE AS A SOURCE OF PLANT NUTRIENTS

Sewage sludge contains all the elements essential for the growth of higher plants. Because nitrogen andphosphorus are the most abundant major plant nutrients in sludge (Metcalf and Eddy, 1991), its agricultural use isalmost exclusively as a supplemental source of nitrogen and/or phosphorus fertilizer.

SOIL, CROP, AND GROUND WATER EFFECTS 63

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Nitrogen

Typically, treated sludges include about 1 to 6 percent nitrogen on a dry weight basis (Metcalf and Eddy,1991; Dean and Smith, 1973). By contrast, nitrogen in commercial fertilizers range from 11 to 82 percent (Lorenzand Maynard, 1988). The nitrogen in treated sludge occurs in both organic and plant-available inorganic forms.The relative proportions of each depend upon the way sludges are processed. In anaerobically digested liquidsludges, microbial oxidation of the organic materials is incomplete, and the nitrogen occurs in both solubleammoniacal and insoluble organic forms, primarily, in microbial cells (Broadbent, 1973). In aerobically digestedsludges, microbial oxidation is greater and there is less residual organic nitrogen than in anaerobically digestedsludges. Ammoniacal nitrogen is about 10 percent of the total nitrogen in aerobically digested sludge and about 30percent of the total nitrogen in anaerobically digested sludge (Linden et al., 1983). In aerobically digested sludge,the ammoniacal nitrogen is further oxidized to nitrate, of which part is lost to wastewater when sludge isdewatered. Likewise, when anaerobically digested sludges are dewatered, part of the ammoniacal nitrogen is lostwith the water.

Where sludges are used as a source of nitrogen, the nitrogen application rates should not exceed theagronomic rate (a rate equivalent to the amount of fertilizer nitrogen applied to the soil for the crop grown). Aswith any fertilizer, nitrogen that leaches beyond the root zone could contaminate ground water. To determine thequantity of sludge needed for the crop's nitrogen requirement, it is important to know the relative proportions ofinorganic and organic nitrogen. The inorganic forms of nitrogen (nitrate and ammonium) are immediatelyavailable to the crop. Organic forms of nitrogen are not available to the crop and must first be mineralized bymicroorganisms to inorganic forms. The rate of mineralization depends on a number of factors including sludgetype, carbon-to-nitrogen ratio of the soil and/or sludge, climate, soil type, and water content. The rate ofmineralization of sludge-borne organic nitrogen in soil ranges from a high of essentially 100 percent per year to alow of a few percent during the initial year of application (Parker and Sommers, 1983). Nitrogen not mineralizedduring the initial cropping year is mineralized in subsequent years, but usually at a diminishing rate. In general,mineralization rates of organic nitrogen in composted and dry sludges are less than those of liquid sludges anddewatered sludge cake.

A theoretical example is presented in Table 4.1 of a 5-year change in available nitrogen from applying asludge containing 2 percent organic and 1 percent inorganic nitrogen. In the example, the organic nitrogenmineralization rate is 40 percent the first year, and this rate is reduced by 50 percent each succeeding year (thecomputation assumes that the only removal of nitrogen from the system is through plant uptake). In this example,the amount of plant-available nitrogen from 5 annual applications of 1 ton of sludge increases from 18 kg/ton to 22kg/ton, and the amount of sludge required to supply 180 kg available nitrogen per ha decreases from 10 tons to 8.2tons from year 1 to year 5. The example shows the importance of mineralization of organic nitrogen in succeedingyears following the application. If organic nitrogen mineralization is not properly accounted for, overfertilizationmay occur that will subsequently lead to nitrogen leaching.


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TABLE 4.1 Effect of Organic Nitrogen Mineralization on Plant-available Nitrogen (N) from Sludge Applications.a

Year Available inorganic N(kg/ton)

Available organic N(kg/ton)

Total available N (kg/ton) Sludge requiredb (tons)

1st 10 8.0 18.0 10.0

2nd 10 10.4 20.4 8.8

3rd 10 11.4 21.4 8.4

4th 10 11.8 21.8 8.3

5th 10 12.0 22.0 8.2

a The analysis assumes that sludge contains 1.0 percent inorganic and 2.0 percent organic nitrogen. Mineralization rate is 40 percent thefirst year, reduced by one-half in each succeeding year (40, 20, 10, 5).b Amount of sludge required to supply 180 kg available nitrogen per hectare.

Phosphorus

Commercial fertilizers typically contain between 8 and 24 percent phosphorus (Lorenz and Maynard, 1988).By contrast, sludges typically contain between 0.8 and 6.1 percent phosphorus (Metcalf and Eddy, 1991; Dean andSmith, 1973). Like nitrogen, the phosphorus in sludges is present in inorganic and organic forms. The proportionsof each vary and depend on the source of municipal wastewater and on sludge treatment. Unlike nitrogen,inorganic forms of phosphorus are quite insoluble and phosphorus tends to concentrate in the organic andinorganic solid phases. Almost without exception, the amount of phosphorus applied is more than sufficient tosupply the needs of the crop where sludges are applied as a source of nitrogen. For example, a sludge containing1.5 percent phosphorus, applied at a rate of 10 metric tons per ha, would supply 150 kilograms of phosphorus perha. At this application rate, available phosphorus may be excessive in many areas, particularly where animalmanure is plentiful and where phosphorus is well-above levels needed for maximum crop yields. These high levelscould significantly increase the risk of surface water contamination. Based on long-term evaluations of treatedsludge use over periods ranging from 9 to 23 years, the Water Environment Research Foundation (1993) hasrecommended soil phosphorus levels be monitored where sludge applications are used continuously over time, andthat sludge application rates may need to be determined by crop phosphorus levels rather than the nitrogen needsof the crop.

Other Essential Plant Nutrients

In addition to nitrogen and phosphorus, treated sludges contain all other nutrients essential for the growth ofcrops, including calcium, iron, magnesium, manganese, potassium, sodium, and zinc (Linden et al., 1983). Wheretreated sludges are applied according to agronomic rates for nitrogen, many of these essential nutrients, with thepossible exception of potassium, are usually present in amounts adequate to meet the needs of the crop (Chaney,1990).


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TREATED MUNICIPAL WASTEWATER AS A SOURCE OF PLANT NUTRIENTS ANDIRRIGATION WATER

Plant Nutrients

Although treated municipal wastewaters are usually applied as a source of irrigation water for crops, they arealso a source of plant nutrients, especially nitrogen. The concentration of nutrients in wastewaters depends uponthe water supply, the quality of the wastewater, and the type and degree of wastewater treatment. Usually, eachstage in the treatment process reduces the concentration of both nitrogen and phosphorus. Typically,conventionally treated municipal wastewaters contain from 10 to 40 mg of nitrogen per liter and from a few to 30mg of phosphorus per liter (Asano et al. 1985). In the arid southwestern United States, the quantity of irrigationwater required to meet the needs of most crops is the equivalent of about 1 meter depth per ha per crop season.This quantity of treated wastewater, containing typical concentrations of nitrogen and phosphorus of 20 and 10mg/liter respectively, would add 200 kg nitrogen and 100 kg phosphorus per ha. These application rates will meetor, in some cases, exceed the nitrogen and phosphorus fertilizer needs of many crops over the growing season.Further, plants require varying amounts of nutrients and water at different stages in the growth cycle, and thetiming of irrigation may not correspond to when plant nutrients are needed. Wastewater applications at times whenthe plant needs are low can potentially lead to leaching of nitrate-nitrogen and possible contamination of groundwater.

When plant nutrient needs are not in phase with irrigation needs, the presence of nutrients in irrigation watermay interfere with its use. For example, ill-timed and overfertilization with nitrogen can cause excessive growth,reduce crop yield, and encourage weed growth (Asano and Pettygrove, 1987; Bouwer and Idelovitch, 1987). Yieldand crop quality have been harmed by excess nitrogen in many crops, including tomatoes, potatoes, citrus, andgrapes (Bouwer and Idelovitch, 1987). To minimize the undesirable effects of excess nutrients, their levels inreclaimed water should be kept within stipulated guidelines, crops should be selected to match nutrient levels,ground water quality should be monitored, and excess water should be diverted elsewhere (Bouwer andIdelovitch, 1987). In the Water Conserv II wastewater reclamation project in Orlando, Florida, excess water notused by citrus growers is diverted into rapid infiltration basins for disposal (Jackson and Cross, 1993). Because theunderlying aquifer is a drinking water source, it is closely monitored as part of the Conserv II project.

Irrigation Water Quality Concerns

The feasibility of using treated municipal wastewater as a source of irrigation water depends upon its quality.This in turn depends upon the quality of the municipal water supply, the nature of the constituents added duringwater use, and the kind and degree of wastewater treatment. Wastewater constituents that can degrade waterquality for irrigation include salts, nutrients and trace contaminants. Quality criteria for salinity, permeability,specific ion toxicity, and miscellaneous elements are presented in Table 4.2. The effects of reclaimed water on soilchemical properties, including the accumulation of trace contaminants are discussed in a succeeding


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TABLE 4.2 Irrigation Water Quality Criteria

Degree of restriction on usea

Parameter restricting use Diagnostic Measurement (units) None Slight to Moderate Severe

Salinity EC (dS/m)b 0.7 0.7–3.0 >3.0

TDS (mg/1)c 450–2000 >2000

Permeability/ infiltration SAR (mmole/1)1/2d and EC (dS/m)

EC @ SAR 0–6 >1.2 1.2–0.3 <0.3

EC @ SAR 12–20 >2.9 2.9–1.3 <1.3

EC @ SAR 20–40 >5.0 5.0–2.9 <2.9

pH <8.5 >8.5

Phytoxicity (mostly tree crops ornamentals)

With surface irrigation

Sodium SAR (mmole/1)1/2 <3 3.9 >9

Chloride (mg/1) <140 140–350 >350

Boron (mg/1) <0.7 0.7-3.0 >3.0

With sprinkler irrigation

Sodium (mg/1) <70 >70

Chloride (mg/1) <100 >100

Boron (mg/1) <0.7 0.7-3.0 >3.0

With overhead sprinkling only

Bicarbonate (mg/1) <90 90–500 >500

Residual chlorine (mg/1) <1 1.0-5.0 >5

Crop quality/ground water protection

Nitrogen (total N) mg/1 <5 5–30 >30

a Restriction on use but does not indicate that water is unsuitable for use, that there may be a limitation such as crop species or soil typeand special management practices may be necessary for full productive capacity.b Electrical conductivityc Total dissolved solidsd Sodium Adsorption RatioSOURCE: Adapted and condensed from Westcot and Ayers, 1985.

section of the chapter.

EFFECTS OF SLUDGE AND WASTEWATER ON SOIL PHYSICAL PROPERTIES

Organic Matter

Soil organic matter enhances the structural properties of a soil by binding together soil particles intoaggregates or lumps and creating large (non-capillary) pores through which air and


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water more. As land is cropped, soil organic matter is gradually lost, leading to a deterioration of its physicalproperties. Soils under continuous cultivation are very deficient in organic matter because the rate at which organicmatter returns from crop residues is lower than the rate of organic matter decomposition in soils. Where organicmatter is lacking, the less stable soil aggregates easily fall apart in the presence of rain or percolating water; inspite of cultivation, the larger soil pores are lost, soil air decreases, water movement is restricted, the soil becomesmore closely packed, and the bulk density increases.

Water Retention Properties

Generally, the application of sludge increases the capacity of the soil to retain water. The organic carboncontent of sludge may affect water retention either through the direct effect of sludge organic particles themselvesor through its indirect effect on other physical properties (such as bulk density, porosity, and pore sizedistribution). Several researchers have reported an increase in the water retention capacity of soils at field capacity1

and at the wilting point1 following sludge application (Chang et al., 1983; Metzger and Yaron, 1987).

Structure and Aggregation

Sludge, like other organic materials, is less dense than the mineral fraction of soil and can improve thestructure of soil by reducing bulk density and promoting soil aggregation. However, Chang et al. (1983) cautionsthat far greater quantities of sludge than normally needed to supply nutrients for crop growth are required toinduce significant changes in soil physical properties. Low annual application rates (22.5 and 45 metric tons perha) of municipal sludge compost improved agronomic performance, but higher amounts (80 metric tons per ha)were required to significantly change soil physical properties (Chang et al., 1983). Nevertheless, even at lowerannual rates of sludge application (27 metric tons per ha) the bulk density of soils of various textural classes,including fine-textured soils, are reduced (Hall and Coker, 1983; also see Metzger and Yaron, 1987). As withmanures and composts, the organic matter in sludge can increase soil porosity because of improved soilaggregation (Guidi et al., 1983; Pagliai et al., 1981).

The addition of sludge increases the number and size of water-stable aggregates. Increases in aggregateformation, by approximately one-third, were observed by Epstein (1975). This has been substantiated in fieldexperiments on various soil types, in various climates, and with various sludges and composts. Aggregateformation is the result of both chemical and microbial agents.

Aggregate stabilization must occur along with aggregate formation if a permanent increase in soil aggregationis to occur. In a comparative study of four organic materials added

1 Field capacity is approximately equal to the amount of water that is held at -0.33 bar; the wilting point is when plants beginto show moisture stress, defined as -15 bars.


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to soil at 25 metric tons per ha, aggregate stability was increased by 24 percent with sludge, 22 percent withmanure, 40 percent with alfalfa, and 59 percent with straw (Martens and Frankenberger, 1992). Anaerobicallydigested sludges provided the best stabilizing effect compared to other sludge treatment processes (Pagliai et al.,1981).

Water Transmission Properties

Organic matter in sludge and wastewater can impede infiltration and aeration by temporarily plugging thesoil surface. However, the net effect of organic matter on soil aggregation, as explained above, is improved soilstructure, which enhances water transmission, water infiltration and, in some instances, reduces the soil'ssusceptibility to erosion.

Under certain conditions, the levels of sodium, calcium, and magnesium in treated effluents can adverselyaffect soil structure and worsen the soil's infiltration, friability, and tillage characteristics. Sodium, when present inhigh concentrations relative to calcium and magnesium, can cause dispersion of soil aggregates leading to reducedinfiltration and permeability. The degree to which the various concentrations of sodium may affect soil structure isrelated not only to concentrations of calcium and magnesium but also to the salinity of the effluent. Techniquesused to predict the effects of sodium on infiltration and permeability of water are based on the Sodium AdsorptionRatio (SAR), a ratio of the concentration in water of sodium to the square root of the sum of the concentrations ofcalcium plus magnesium (all concentrations are expressed in millimoles per liter). Waters with high SAR but lowsalinity disperse the soil, making it less friable, harder to work and less permeable to water. For example (as wasshown in Table 4.2), water with a SAR of 12, a total dissolved solids (TDS) level of about 1200 (at an ElectricalConductivity [EC] of about 1.9 deci Siemens per meter [dS/m]) causes no permeability or infiltration problems,while water with a SAR of 3 and a TDS of about 200 (at an EC of about 0.3 dS/m) causes severe permeabilityproblems. The salinity of soil water also affects the growth of crops through its effect on water availability(Bouwer and Idelovitch, 1987). Plants vary in their tolerance of soil salinity (Maas, 1990).

EFFECTS OF SLUDGE AND WASTEWATER ON SOIL CHEMICAL PROPERTIES

Biologically stabilized sewage sludge contains an average of approximately 50 percent organic matter on adry weight basis. Following addition to soil, the sludge undergoes decomposition to carbon dioxide, water, lowmolecular weight soluble organic acids, residual organic matter and inorganic constituents. Although most of theorganic fraction of the sludge is converted to carbon dioxide and water, some becomes part of the stable soilhumus layer (Boyd et al., 1980; Hernandez et al., 1990) and serves to increase the soil's net negative charge and itscation exchange capacity (CEC) (National Research Council, 1977; Thompson et al., 1989). CEC is a measure ofthe capacity of the soil to retain cations. A high CEC is desirable because it lessens or prevents essential nutrientloss by leaching (Broadbent, 1973; National Research Council, 1977). Collectively, constituents released fromsludge following decomposition and present in wastewater may be put into four groupings: 1) the more soluble


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cations, anions and molecules, 2) trace elements which form sparingly soluble reaction products, 3) potentiallyharmful inorganic chemicals, and 4) potentially harmful organics.

Soluble Cations, Anions, and Molecules

The soluble cations, anions, and molecules found in effluents and sludge, and which are of concern inagricultural operations, generally include potassium, sodium, calcium, magnesium, chloride, sulfate, nitrate,bicarbonate, selenate, and boron (as boric acid and borate) in lesser concentrations. All of the above are absorbedby plants and those which are essential contribute to the nutrient-supplying power of effluents and sludges. Theyenter into ion exchange equilibria and those of lesser affinity are leached away by drainage water. Because boricacid is usually uncharged and is weakly adsorbed, it normally is leached to levels safe for most crops where wateris applied in excess of evapotranspiration (Keren and Bingham, 1985). Above concentrations of about 0.7 mg/literin irrigation waters, boron may be toxic to sensitive plants (Maas, 1990). Consequently, precautions must be takento insure that the boron concentrations in the soil solutions of sludge-amended soils and soils irrigated withmunicipal wastewater do not exceed this critical level for sensitive crops. Tolerant crops (e.g. cotton) normallywithstand irrigation waters containing boron concentrations as high as 10 mg/liter without damage (Maas, 1990).

As with normal irrigation practices, salts in reclaimed wastewater need to be managed to preserve theproductivity of the soil. Typical concentrations of salts in treated effluents are within accepted criteria for irrigationwater quality (see Table 2.1); however, their concentration can vary widely. Unless salts are removed from theroot zone by plants or leaching, they accumulate and eventually reach a level that will prevent the growth of allbut the most tolerant plants. Even under the most ideal conditions, plants remove less than 10 percent of the saltsapplied through irrigation water (Oster and Rhodes, 1985). Therefore, to sustain growth, salts must be leached fromthe root zone. In temperate and humid regions where irrigation is practiced only during dry periods, precipitationis usually sufficient to leach salts to an acceptable level. However, in semiarid and arid regions, continuedirrigation in the absence of leaching will lead to an accumulation of salts in the soil profile to levels that willinhibit the growth of crops. This problem is usually circumvented by adding more water than is used by the crop.The quantity of water in excess of crop requirements is referred to as the leaching requirement. Methods used tomanage irrigation waters of varying quality to avoid the accumulation of salinity problems are outlined by Kruseet al. (1990).

Trace Elements

Following organic matter decomposition, trace elements from wastewater and sludge are released and formsparingly soluble reaction products. These trace elements include arsenic, cadmium, copper, cobalt, nickel, lead,selenite-selenium, molybdate-molybdenum, and others. Because of their sparingly soluble nature and their limiteduptake by plants, they tend to accumulate in the surface soil and become part of the soil matrix (McGrath et al.,1994). With


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repeated applications of wastewater, and particularly sludges, these elements could accumulate to levels toxic toplants (Chang et al., 1992) and soil organisms (McGrath et al., 1994). They could also accumulate in crops wherethey could, in turn, build up to potentially harmful levels in humans, domestic animals, and wildlife that consumethe crops (Logan and Chaney, 1983). EPA developed soil concentration limits considered safe for agriculturalcrops in its Part 503 Sludge Rule (EPA, 1993a) and these limits are presented in Chapter 7.

In general, crops grown on acid soils accumulate higher concentrations of most trace elements in their tissuesand are more susceptible to phytotoxicity than are crops grown on neutral or calcareous soils. Because repeatedsewage sludge applications lead to accumulations of trace elements in soil, concern has been expressed overpossible adverse effects associated with the use of sludge on soils that are acid or that may become acid (McBride,1995). In an attempt to address this concern, Ryan and Chaney (1994) compared the pH distribution of soils usedby EPA in the development of the Part 503 Sludge Rule with pH values of all U.S. soils (as compiled by Holmgrenet al. 1993). From this comparison it was evident that acid soils were well represented in EPA's analysis. Anadditional safeguard arises from a set of conservative assumptions used in EPA's risk assessment. In setting thestandards for trace elements, EPA assumed a cumulative application limit of 1000 metric tons of dry sludge perha. Because sludge application rates used in most of the available research studies were lower than this, EPA used alinear regression technique to extrapolate crop uptake to the limit of 1,000 metric tons. Chaney and Ryan (1992)showed that crop uptake usually reaches a plateau with increasing sludge application and that the actual cropuptake of trace elements should be far lower than predicted by the linear regression values used by EPA. Finally,in normal agricultural practice, crops grown in extremely acid soils with excess zinc, copper, and nickel wouldshow visual phytotoxicity symptoms. In practice, when these symptoms are observed, the soil is limed to correctthe problem. In fact, problems associated with soil acidity are normally corrected through routine managementoperations because, almost without exception, acid soils are limed prior to cropping. This neutralizes acidity toavoid phytotoxicity from naturally occurring aluminum present in the soil (Pearson and Adams, 1967). Therefore,as long as agricultural use of treated sludges and wastewater is in keeping with existing regulations and soundagronomic practices, the possibility that trace elements applied from this practice would adversely affect the yieldor wholesomeness of crops is remote.

Concerns have been expressed about what may happen once a site has reached its cumulative limit for metalsand sludge application stops (McBride, 1995). The chemical properties of the soil will likely change over time.The availability of certain trace elements may increase and potentially cause phytotoxicity problems and/or causegreater bioaccumulation of trace elements in crops. While there is little published information on this long-termproblem, the city of Chicago has accumulated soils and crop data on both reclaimed strip-mined fields and naturalsoils following termination of sludge applications. Table 4.3 shows an example of some data collected on organiccarbon, zinc, cadmium, and copper from seven fields that had received an average of 226 tons per acre of sludgefrom 1972 through 1984, where monitoring had continued to the present. Additional research is needed in thisarea, but these preliminary results indicate that trace elements are not necessarily more available for periods of upto 10 years following cessation of sludge applications.


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TABLE 4.3 Organic Carbon and Availability of Zinc, Cadmium, and Copper After Cessation of Long-Term SludgeApplication

Year Organic Carbon % Zinc Cadmium Copper

soila cornb soil corn soil corn

1984 4.4 747 26.0 56.5 0.27 295 2.05

1985 4.4 668 33.0 58.3 0.26 321 0.95

1986 4.8 655 26.8 49.8 0.07 261 1.29

1987 4.2 701 25.5 53.5 0.20 295 2.59

1988 4.0 614 35.5 45.9 0.07 240 1.62

1989 3.9 689 33.5 45.5 0.38 255 2.57

1990 4.3 586 33.5 46.2 0.11 232 1.94

1991 4.1 584 33.0 45.8 0.05 242 1.62

1992 4.1 676 33.0 52.1 0.17 289 0.97

1993 3.9 635 20.0 49.6 0.11 275 2.00

a Zinc, cadmium, and copper soil measurements are 0.1 M HCl extractable concentrations in mg kg-1 for the top six inches of soil asmeasured annually on samples from each field.b Corn grain concentrations in mg kg-1

Note: Farm fields received an average of 226 tons/acre of sludge from the Metropolitan Water Reclamation District of Greater Chicagofrom 1972 through 1984. None of the fields have received sludge since 1984. The cumulative loading rate for Zn, Cd and Cu was 1,532,827 and 127 kg ha-1 (1,367, 738, and 113 lb/acre), respectively.SOURCE: Granato, 1995.

Accumulation of Potentially Harmful Inorganic Chemicals in Soils and Crops

Treated municipal wastewaters rarely contain harmful trace elements at concentrations in excess of criteriaestablished for irrigation water (as was shown earlier in Table 2.1). Therefore, where industrial pretreatmentprograms are effectively enforced, it would seem reasonable to permit treated municipal wastewaters that meetirrigation water quality criteria to be used for crop irrigation. Assuming this to be the case, municipal wastewaterapplied at the limits prescribed for irrigation water at the rate of 1.5 m/ha (per growing season) should addrelatively minor amounts of trace elements.

The concentrations of trace elements in sewage sludges vary, depending on the contributions from industriesand households to the common sewer system and the effectiveness of industrial pretreatment programs (seeChapter 3). Ranges of trace elements based on the EPA 1990 National Sewage Survey (NSSS) are presented inTable 4.4 from Kuchenrither and Carr (1991). Using these data for a typical sludge applied at 10 metric tons perha, one can compute annual soil loading of trace elements. Data presented in Table 4.5 show annual loading oftrace elements with compositions at the 50th, 95th, and 98th percentiles compared to typical soil concentration andthe EPA cumulative loading limits from the Part 503 Sludge Rule. Although applications of sludges withcompositions at the 95th and 98th percentile add substantially to the


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TABLE 4.4 Summary of Results for Regulated Inorganic Pollutants From the EPA 1990 National Sewage Sludge Survey

Pollutant Number of Times Detecteda Mean (mg/kg) Minimum (mg/kg) Maximum (mg/kg)

Arsenic 194 12.4 0.3 316

Cadmium 194 65.5 0.7 8,220

Chromium 231 258 2.0 3,750

Copper 239 665 6.8 3,120

Lead 213 195 9.4 1,670

Mercury 184 4.1 0.2 47.0

Molybdenum 148 13.1 2.0 67.9

Nickel 201 77.0 2.0 976

Selenium 163 6.2 0.5 70.0

Zinc 239 1,693 37.8 68,000

a The values represent the number of times the chemical was detected in samples taken from 209 wastewater treatment plants. Plants wererandomly selected from all regions of the U.S. The total number of samples is 239 because of multiple samples taken at some plants.SOURCE: Adapted from Kuchenrither and Carr, 1991.

background concentrations in soils, additions are well within U.S. EPA limits. In the most limiting cases ofcopper, lead, and zinc, a sludge with an element concentration equal to the 95th percentile could be appliedannually at 10 metric tons per ha for a period of about 75 years before regulatory limits would be reached.

Actual experience at numerous sewage sludge land application sites has indicated that uptake of metals byplants has been minimal. Bray et al. (1985) analyzed three years of silage crop on land amended each year bymunicipal sludge at moderate to high rates (15–90 metric tons per ha). The silage contained elevated though notexcessive levels of cadmium and zinc, but elevated levels were not observed for the other 12 elements tested,including arsenic, chromium, lead, mercury, and selenium.

In developing the Part 503 Sludge Regulations, EPA conducted an extensive review of trace element uptakeby crops in relation to amounts added in the form of sewage sludge (EPA, 1993a; 1993b). Table 4.6 lists uptakeslopes for different food crops and shows that crops differ substantially in their tendency to bioconcentratesludge-borne trace elements added to soils. An uptake slope is calculated as the concentration of a chemical inplant tissues in (mg/kg) divided by the amount of chemical added to the soil (in kg/ha). Based upon the geometricmean of uptake slope values, the elements arsenic (As), copper (Cu), lead (Pb), mercury (Hg), and nickel (Ni)consistently show the lowest uptake values across all food groups. The elements cadmium (Cd), selenium (Se),and zinc (Zn) have the highest uptake values in the majority of the food


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TABLE 4.5 Annual Loading of Trace Elements for Sludges With Compositions Equal to the 50th, 95th and 98th PercentileFrom the National Sewage Sludge Survey When Applied at a Rate of 10 m tons/ha Compared to Typical SoilConcentrations and the EPA Loading Limits. All Values are in kg/ha.

Element Annual Loading at Percentile Compositions Typical Concentration in Soil EPA Cumulative LoadingLimit

50th 95th 98th

Arsenic 0.10 0.40 0.54 12.0 41

Cadmium 0.07 0.15 0.58 0.15 39

Chromium 1.2 5.0 10.0 200.0 3,000

Copper 7.4 21.0 35.0 40.0 1,500

Lead 1.4 4.0 8.0 30.0 300

Mercury 0.05 0.19 0.38 0.06 17

Nickel 0.04 2.0 2.9 80.0 420

Selenium 0.05 0.19 0.27 0.4 100

Zinc 12.0 35.0 60.0 100 2,800

groups, although the uptake slopes are reasonably low in most cases. Molybdenum (Mo) is unique in that itsuptake slope is very high for leguminous vegetables. The elements copper, molybdenum, and zinc are essential forthe growth of plants, so these data indicate that sludge could correct deficiencies of these elements. The elementcadmium, if present in the human diet in sufficient quantities over extended periods of time (decades), is a chronictoxin (Kostial,1986); molybdenum and selenium are toxic to wildlife and domestic animals if consumed abovecritical levels (Mills and Davis, 1986; Levander, 1986). The public health concerns about exposure to traceelements through the consumption of crops grown on sludge-amended soils are discussed in Chapter 6.

Accumulations of Potentially Harmful Organics in Soils and Crops

Organic chemicals, when added to the soil may volatilize, decompose, or be adsorbed. Consequently, onlythose that are nonvolatile and are relatively resistant to decomposition will accumulate in soils. Most organiccompounds found in treated municipal wastewater occur at concentrations of less than 10 mg/liter, andaccumulation in soil from this source is usually so small that it is below the limits detectible by conventionalanalytical methods (O'Connor et al.,


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TA

BL

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Upt

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: EPA

, 199

3b.


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1991, Webber et al., 1994). Based upon the 99th percentile concentration from the NSSS, EPA computedannual loading for 12 reasonably persistent organic chemicals. Available evidence indicates that most traceorganics are either not taken up or are taken up in very low amounts by crops (O'Connor et al., 1991, EPA,1993b). A discussion of possible implications and health consequences of toxic organic compounds in sludges ispresented in Chapter 6.

EFFECTS OF SLUDGE ON SOIL MICROORGANISMS

Soil microorganisms include bacteria, actinomycetes, fungi and algae. They are important in thedecomposition of organic matter and in the cycling of plant nutrients such as nitrogen, phosphorus, and sulfur.Metal accumulations in soils associated with the long-term applications of sewage sludge have been shown toaffect microbial activity and biomass, biological nitrogen fixation, and vesicular-arbuscular mycorrhizae (Giller etal., 1989; McGrath et al., 1988; McGrath et al., 1994; Smith, 1991). Vesicular-arbuscular mycorrihizae refers tothe symbiotic association between plants and certain fungi, in which the fungi obtain carbohydrates and the plantsobtain nutrients such as phosphorus and zinc for growth.

Microbial Biomass and Activity

The application of sewage sludge will temporally increase microbial populations due to the addition of anexogenous food supply. Depending upon the carbon to nitrogen (C/N) ratio of the added material, the demands ofthe increased microbial population for nitrogen could reduce the plant-available nitrogen to levels that aredeficient for crop growth (Alexander, 1977). This process, referred to as immobilization, occurs when the C/Nratio in the sludge-soil mixture is about 20 or more and microbes convert inorganic nitrogen to organic nitrogen—a form unavailable to crops (Alexander, 1977). However, immobilization of nitrogen is usually temporary. Asdecomposition proceeds, carbon is volatilized to carbon dioxide, and as the C/N ratio becomes less than about 20,mineralization of the organic nitrogen exceeds immobilization, and excess inorganic nitrogen becomes available toplants.

The accumulation of metals following long-term applications of sewage sludge has been observed to reducelevels of microbial biomass (Brookes et al., 1986b). In a long-term field experiment that compared sludge-amended soils to manure-amended soils, McGrath et al. (1994) reported microbial biomass levels in the high-metal sludge-treated soils to be approximately half those of the manure-treated soils. Similar observations weremade by Boyle and Paul (1989) who also reported increased levels of nitrogen in soil biomass following eightyears of sludge application. A one time high-rate sludge application has also been reported to decrease soilbiomass (Stark and Lee, 1988).

Biological Nitrogen Fixation

The accumulation of metals in soils following long-term applications of sewage sludge


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has been reported to adversely affect the symbiotic relationship between certain strains of rhizobia (McGrath etal., 1994; Giller et al., 1989). McGrath et al. (1988) observed lesser concentrations of nitrogen and decreasedyields of white clover in a soil that had received sludge applications over a period of 20 years. Clover root nodulesin the treated group were smaller and ineffective in nitrogen fixation. Clover rhizobia isolated from high metal-contaminated soil were ineffective in nitrogen fixation (Giller et al., 1989). Nitrogen fixation was restored byinoculation of the soil with large numbers of effective rhizobium of the same strain (greater than 10,000 cells pergram of soil) followed by incubation in a moist condition for two months (McGrath et al., 1994). The authorsconcluded that clover rhizobia were unable to survive in the free-living state outside the protected root nodule inmetal-contaminated soils.

The inhibition of rhizobium bacteria following sludge applications is inconclusive, and other studies haveshown little or no effect of sludge on nitrogen fixation. Heckman et al. (1987), for example, examined the effectsof sludge-amended soil on the symbiotic fixation of nitrogen by soybean. They found no effect of sludge metals onnitrogen fixation at one site but observed a decrease in the amounts of nitrogen fixed where high metal sludgeswere applied at another site. Kinkle et al. (1987) studied soybean rhizobia in soils that had received sludge 11years earlier. They observed no long-term detrimental effect of sludge applications on soil rhizobial numbers andno shift in serogroup distribution. Similarly, Angle and Chaney (1989) observed no effect of sludge applicationson rhizobia. More recently Ibekwe et al. (1995) reported reduced nodulation and ineffective symbiosis for alfalfa,white clover, and red clover grown in sludge-amended soils (pH equal to or less than 5.2). However, theinvestigators observed no effect on plant growth, nodulation, and nitrogen fixation when these legumes weregrown in sludge-amended soils maintained at pH 6.0 and greater.

Long term applications of sewage sludge resulting in metal accumulations in surface soils have been shown toreduce nitrogen fixation by free-living heterotrophic bacteria (Brookes et al, 1986a; Lorenz et al., 1992;Martensson and Witter, 1990). In an experiment where sludge-treated soils were compared to manure-treatedsoils, nitrogen-fixing activity by diazotrophs in the sludge-treated soil was decreased to 2 percent of that of themanure-treated soil. Lorenz et al. (1992) also observed reduced nitrogen fixation in plots treated with sludgecompared to plots treated with farmyard manure. Nitrogen fixation by cyanobacteria (blue-green algae) has alsobeen reported to be reduced in soils having a history of repeated sludge applications as compared to soils with along history of farmyard manure applications (Brookes et al., 1986a).

Symbiotic functions between plants and soil microbes are negatively impacted only if the soil microbes affectuptake of nutrients by the associated plants. Studies on vesicular-arbuscular mycorrhizas (VAM)-plantassociations in sludge-treated soils are confounded by the rather large amounts of phosphorus added with sludgeand the effect of soil pH on VAM, both of which in addition to the effect of metals, could inhibit infection.Available information suggests that sludge applications to soil act to delay rather than suppress mycorrhizalinfection (Koomen et al., 1990).


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A tractor spreading sewage sludge on a stubble field before the growing season (photo courtesy of Robert Bastian,U.S. Environmental Protection Agency).

EFFECTS ON GROUND WATER

Because municipal wastewater contains only traces of pesticides (O'Connor et al., 1991; Kuchenrither andCarr, 1991), land application of treated wastewater effluents and sludge presents a much smaller hazard ofpesticides than does the usual, direct application of pesticides to crops for the control of pests.

Nitrate pollution of ground water is often reported as an effect of excessive application of conventionalfertilizers to crops (Hallberg and Keeney, 1993). As described earlier in this chapter, nitrate pollution ofgroundwater from application of wastewater effluent and sludge can be controlled by the same nutrientmanagement techniques used in traditional agriculture.

The potential for ground water contamination by microorganisms, trace elements and toxic organiccompounds from wastewater and sludge is evaluated below. (Chapters 5 and 6 discuss other public health effectsof these contaminants.)

Pathogenic Microorganisms

There are three kinds of microorganisms in sewage which are of concern for their effects on human health:bacteria, viruses, and parasites. All have been found in treated secondary effluent


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and sludges. Wastewater irrigation can potentially transport bacteria and viruses to ground water under certainconditions, as described below. In contrast, because bacteria and viruses in sludge are strongly sorbed to sludgesolids, they are not usually desorbed in the soil, and are not likely to be transported to ground water. Helminthcysts and worm eggs are reported to be too large to be transported to ground water (Gerba, 1983).

Viruses are a special concern in wastewater irrigation because virus particles are small, may percolate throughsoil, and may persist for months in the soil environment (Gerba, 1983). Using traditional methods of virussampling and assay of water from soil lysimeters at sites irrigated with undisinfected secondary wastewatereffluent, Moore et al. (1981), have found coliphage virus particles at a depth of 1.37 meters. Using more sensitivedetection methods, several ground water samples were taken 27.5 meters below wastewater soil application sitesand were found to be positive for animal viruses. In the same study, the test soil site receiving disinfectedwastewater had only one sample which was positive for viruses, significantly less than soils irrigated withundisinfected wastewater effluent (Goyal et al., 1984).

Disinfection appears to be advisable in preventing ground water contamination by viruses from irrigation withtreated municipal wastewater. In the context of food crop production, EPA guidelines recommend a minimum ofsecondary treatment plus disinfection (EPA, 1992). Current state regulations for reclaimed water use on crops varydepending on water quality and process requirements, site restrictions, monitoring, and crop type allowed. Of the18 states that regulate irrigation of food crops with reclaimed water, only 3 (Arkansas, Nevada, and Michigan) donot have requirements for disinfection or criteria for microbiological water quality; however other restrictions orground water monitoring may apply (see discussion of state regulations in Chapter 7).

In a summary of virus removal from treated wastewaters, Asano (1992) has estimated that undisinfectedeffluent has approximately 90 percent of viruses removed (1 log removal) from sewage as a result of primary andsecondary wastewater treatment processes. Effluent disinfection accounts for an additional 2 to 5 logs removal,that is, a total of 99.9 to 99.999 percent virus removal. When combined with natural soil sorption processes, virusremoval from disinfected effluent applied to soils for the purpose of groundwater recharge has been estimated tobe 12.6 to 17 logs of reduction. Using a risk assessment approach, Asano et al. (1992) developed an exposurescenario that uses the nearest well to a ground water recharge site containing 50 percent reclaimed wastewater thathas percolated through three meters of soil for six months. The most exposed individual is assumed to consumetwo liters per day of this wellwater, equivalent to 1 liter per day of reclaimed wastewater. The authors haveestimated that the lifetime risk of an individual contracting a single infection from poliovirus or echovirus fromdrinking ground water recharged with disinfected (tertiary treated) wastewater effluent was very low, in the rangeof 10-6 to 10-9. While not the subject of this report, the use of treated municipal wastewater as a source for groundwater recharge has been evaluated by the National Research Council (1994). Its report concludes that wheretreated municipal wastewater is used to recharge ground water that is a potable water supply, uncertainties remainconcerning the transport and fate of viruses in ground water.

Bacteria that are used as indicators of wastewater contamination (fecal coliform and fecal streptococci) havebeen found in soil water at a depth of 1.37 meters below fields irrigated with treated but undisinfected wastewatereffluent. Bacterial counts in lysimeter water ranged from


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2 to 370 viable cells per 100 milliliters water for fecal coliform bacteria and from approximately 1 to 77 fecalstreptococcus bacteria per 100 milliliters of water (Moore et al., 1981).

In summary, application of treated wastewater effluents to soils may pose some risk of ground watercontamination by viruses and bacteria, but that risk is minimized to extremely low levels by disinfection ofreclaimed wastewater and by slow infiltration rates (Asano et al., 1992; Gerba, 1983).

Heavy Metals

Through cation exchange, chemical exchange, chemical sorption, precipitation, and complexation reactions,metallic ions are readily removed from wastewater and are concentrated in sludges. Soil particles act to furthersequester most heavy metals, and this preference of metals for particulates has been observed often in agriculturalsoils. (Chang and Page, 1983; Pettygrove and Asano, 1985; Gallier et al., 1993). Therefore heavy metal cationswould not be expected to leach out of the unsaturated soil zone into ground water. In fact, of the toxic heavymetals regulated under the Part 503 Sludge Rule, (EPA, 1993b), a scientific peer review panel suggested that therisk of ground water contamination be used only to determine the heavy metal standard for hexavalent chromium(Chaney and Ryan, 1992). Hexavalent chromium is an unstable and rare form of chromium, and is rapidly reducedin most environmental conditions to its trivalent form, which is quite immobile in soils and not expected to leachto ground water.

Heavy metals from sludges may remain in soils for years after application. However, when sludges areapplied to soils at rates controlled by agronomic nutrient uptake rates, transport of heavy metals from sludges toground water is unlikely unless the sludges have unusually high levels of metal ions (Logan and Chaney, 1983).

Toxic Organic Compounds

PCBs and detergents are the only classes of synthetic organic compounds that occur in municipal wastewatersludges and effluents in concentrations higher than those in conventional agricultural irrigation water or soiladditives (O'Connor et al., 1991; Brunner et al., 1988; Giger et al., 1987; Furr et al., 1976). In municipal treatmentplants, both PCBs and detergents are concentrated into the sludge fraction.

PCBs have been found in sludges from municipal wastewater treatment plants, especially those receivingindustrial waste discharges or urban storm drainage. Furr et al. (1976) reported concentrations of PCBs from singlesample analyses of sludges from major cities to be in the range of less than 0.01 mg/kg dry weight for SanFrancisco, California to 23.1 mg/kg for Schenectady, New York. An average PCB concentration in sludges fromthe 15 cities in this survey was 4.8 mg/kg dry weight, with PCBs detected in 87 percent of the samples. Morerecently, the NSSS reported that PCB concentration in sludges averaged 3.2 mg/kg dry weight, and PCBs weredetected in approximately 10 percent of the samples from about 200 treatment plants (Kuchenrither and Carr,1991).

PCBs have a strong affinity for particulate material and, under certain circumstances, can


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be volatilized. They are not very soluble, and it is unlikely that PCB compounds would be transported to groundwater from the unsaturated soil zone. Gan and Berthouex (1994) have studied sludge application sites from theMadison (Wisconsin) Metropolitan Sewerage District from 1985 to 1990. They report that there were nomeasurable PCBs in runoff water from these sites. From their study, it seems that while PCBs may persist in thesoil itself and may be taken up by plants, they are not a significant risk for ground water contamination.

Testing for 330 toxic organic compounds in the NSSS found infrequent occurrence in the 209 POTWssampled. However, one organic compound, bis(2-ethylhexyl) phthalate, was detected in 90 percent of the sampleswith an average concentration of 108 mg/kg dry weight (Kuchenrither and Carr, 1991). Bis(2-ethylhexyl)phthalate is thought to sorb very strongly to soil, and therefore would not be expected to leach into ground water.Also, the compound is relatively biodegradable with an estimated half-life in soil ranging from 5 to 23 days(Howard et al., 1991). Phthalates are commonly used as plasticizers, such as in polyvinylchloride, and over onemillion metric tons of phthalates are produced annually worldwide. Because phthalates are so ubiquitous in theenvironment, laboratory-derived phthalates are reportedly a frequent source of errors in sample analyses(Schwarzenbach et al., 1992).

Detergent compounds, including surfactants like linear alkylbenzene sulfonates and nonylphenol ethoxylatesand binders like nitriloacetate, have been found in sludges in relatively high concentrations, in the range of 0.5 to 4g/kg dry weight (Brunner et al., 1988; Giger et al., 1987). However, in field and laboratory tests, it has beenobserved that detergents are rapidly removed from the soil-root zone by biodegradation, and are not transportedout of the unsaturated soil zone by leaching (Holt et al., 1989).

In summary, a few toxic organic compounds and detergents have been found in sludges; however, becausethey are either biodegradable in soils or sorb strongly to soil particles, these compounds are not a risk for groundwater contamination. Overcash (1983) has stated that leaching of toxic organic constituents to ground water willnot occur when application rates for either treated wastewater effluent or sludge to agricultural soils are controlledby crop water and nutrient demands. However, it is cautioned that soils should be allowed to drain after eachapplication and that the ground water table should be more than 0.3 to 1 meter (about 1 to 3 feet) from the soilsurface.

LANDSCAPE-LEVEL CONSIDERATIONS

The foregoing discussion is mainly focused on the application of municipal or wastewater sludge on singlefields or farms. However, the solution to both pollution problems and the sustainability of agriculture depends onconducting investigations at broader scales, such as communities and watersheds. For example, the impact ofagricultural nonpoint pollution on streams and water supplies depends upon the combined effects of all farmpractices within a watershed rather than the application of sludge to one field for one year (for example, seeBarrett et al., 1990; Barrett and Bohlen, 1991). Indeed, Barrett (1992) noted that a new field of study—agrolandscape ecology—must evolve if society is to develop and manage agriculture in a sustainable and cost-effective manner for future generations. As alternative agricultural (National Research Council, 1989) gainsacceptance, the role of sludge at these levels of integration


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should be evaluated.

SUMMARY

Municipal sewage sludge can be used as a source or supplemental source of nitrogen and phosphorous in theproduction of crops. Sludge also contains all other essential plant nutrients and, when used as an nitrogen sourceat agronomic rates, will usually satisfy crop requirements for all essential nutrients, except possibly potassium.The salts, nitrogen, trace elements and trace organics in sludge and wastewater effluents need to be managedproperly to avoid damage to the soil, crop, consumer of the crop, and ground water. If the constituents from sludgeand wastewater applications are not removed in the harvested crop, volatilized, or degraded, they may escape theroot zone and leach to ground water. The accumulation of metals in sludge-amended soils may inhibit the activityof certain strains of clover rhizobia and cyanobacteria, and cause reductions in microbial biomass. This may be ofconcern to the sustainability of certain native legume species, but should not impact commercial food cropproduction.

As with the addition to soils of other organic materials, such as hay and animal manures, the addition oforganic matter accompanying successive sludge additions improves the physical properties of soils. This, in turn,exerts a positive influence on water penetration, porosity, bulk density, strength, and aggregate stability.

Concentrations of potentially harmful trace elements in sludges are, almost without exception, greater thantheir concentrations in typical soil. Consequently, sludge applications usually increase the concentrations of traceelements in soils. Because most trace elements are immobile, the added sludge-borne trace elements tend toconcentrate in the surface to the depth of incorporation. Where sludge has been applied to soil according toexisting guidelines and regulations, there have been no reports of phytotoxicity or accumulation of harmful levelsin consumers attributed to the trace elements. Also, as long as agricultural use of treated sludge follows currentregulations, no adverse effects on acid soils or potentially acid soils, are anticipated.

A few toxic organic compounds and detergents have been found in sludges; they are either not absorbed orare absorbed by crops through the root systems in such small amounts that they do not present a threat toconsumers. Some trace organics may be absorbed by the aerial part of the plant through volatilization of thecompounds from the soil surface. However, this pathway does not seem important, particularly where sludges areincorporated into the soil. Because the concentrations of toxic organic compounds in sludge are low and they areeither biodegradable in soils or strongly sorb to soil particles, they do not represent a risk to ground watercontamination. At application rates of either sludge or treated municipal wastewater to agricultural soils that arecontrolled by water or nutrient demand by crops, the leaching of organic wastewater constituents to ground waterwill not occur if soils are allowed to drain after application and the ground water is more than 0.3 to 1 meter fromthe surface.

Where treated municipal wastewaters are used to irrigate crops, users must take into account nutrients(nitrogen and phosphorous) accompanying the water and adjust fertilizer practices accordingly. Under certainsoil-plant systems, it is recommended that soil phosphorus levels be monitored so that the accumulation of soilphosphorus does not exceed crop requirements


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(usually about 150 kg/ha). As long as treated municipal wastewaters meet irrigation water quality criteria and stateregulations governing disease-causing organisms in the water, they should be considered safe for agricultural use.

Treated municipal wastewater effluents and sludge resemble normal irrigation water and manures. Althoughthey may contain some exotic compounds and fertilizer elements in different proportions than an ideal fertilizer,they present no significant hazards to agricultural soils, crops, or the environment if they are applied in quantitiescommensurate with crop needs.

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McBride, M. B. 1995. Toxic metal accumulation from agricultural use of sludge: are USEPA regulations protective? J. Environ. Qual. 24:5–18.

McGrath, S. P., P. C. Brookes, and K. E. Giller. 1988. Effects of potentially toxic metals in soil derived from past applications of sewagesludge on nitrogen fixation by Trifolium repens L. Soil Biol. Biochem. 20: 415–424.

McGrath, S. P., A. C. Chang, A. L. Page, and E. Witter. 1994. Land application of sewage sludge: Scientific perspectives of heavy metalloading limits in Europe and the United States. Environ. Rev. 2: 108–118.

Metcalf and Eddy, Incorporated. 1991. Wastewater Engineering: Treatment Disposal and Reuse. New York: McGraw-Hill.Metzger, L., and B. Yaron. 1987. Influence of sludge organic matter on soil physical properties. Adv. Soil Sci. 7: 141–163.Mills, C. F., and G. K. Davis. 1986. Molybdenum. Pp. 429–463 in Trace Elements in Human and Animal Nutrition. 5th edition. Walter K.

Mertz, ed. San Diego, Calif.: Academic Press, Inc.Moore, B. E., B. P. Sagik, and C. A. Sorber. 1981. Viral transport to ground water at a wastewater land application site. Jour. WPCF 53:

1492–1502.National Research Council. 1977. Multimedium Management of Municipal Sludge. Washington, D.C. National Academy Press.National Research Council. 1989. Alternative Agriculture. Washington, D.C.: National Academy Press.National Research Council. 1994. Ground Water Recharge Using Waters of Impaired Quality. Washington, D.C.: National Academy Press.O'Connor, G. A., R. L. Chaney, and J. A. Ryan. 1991. Bioavailability to plants of sludge-borne toxic organics. Rev. Environ. Contam. Toxicol.

121: 129–153.Oster, J. D., and J. D. Rhodes. 1985. Water management for salinity and sodiaty control. Pp. 1–20 in Irrigation with Reclaimed Municipal

Wastewater—A Guidance Manual. G. S. Pettygrove and T. Asano, ed. Chelsea, Mich.: Lewis Publishers.Overcash, M. R. 1983. Land treatment of municipal effluent and sludge: specific organic compounds. Pp. 199–227 in Utilization of Municipal

Wastewater and Sludge on Land, Proc. of 1983 Workshop. A. L. Page, T. L. Gleason, J. E. Smith, Jr., I. K. Iskander, and L. E.Sommers, eds. Riverside: University of California.

Pagliai, M., G. Guidi, M. La Marea, M. Giachetti, and G. Lucamante. 1981. Effects of sewage sludge and composts on soil porosity andaggregation. J. Environ. Qual. 10: 556–561.

Parker, C. F., and L. E. Sommers. 1983. Mineralization of nitrogen in sewage sludges. J. Environ. Qual. 12:150–156.Pearson, R. W., and F. Adams, eds. 1967. Soil Acidity and Lining. Agronomy Monograph No. 12. Madison, Wis.: Am. Soc. Agron.Pettygrove, G. S., and T. Asano eds. 1985. Irrigation with Reclaimed Municipal Wastewater-A Guidance Manual. Chelsea, Mich.: Lewis

Publishers.Pratt, F. P., and D. L. Suarez. 1990. Irrigation water quality assessments. Pp 220–236 in Agricultural Salinity Assessment and Management.

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Schwartzenbach, R. P., P. M. Gschwend, and D. M. Imboden. 1992. Environmental Organic Chemistry. New York: John Wiley & Sons.Smith, S. R. 1991. Effects of sewage sludge application on soil microbial processes and soil fertility. Pp. 191–212 in Advances in Soil

Science. Volume 16. B. A. Stewart, ed. New York: Springer-Verlag.Stark, J. H., and D. H. Lee. 1988. Sites with a history of sludge deposition. Final report on rehabilitation field trials and studies relating to soil

microbial biomass (LDS 9166 SLD). Final Report to the Department of the Environment. Report No. DoE 1768-M. Water ResourcesCenter, Marlow, U.K.

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5

Public Health Concerns About Infectious Disease Agents

The infectious disease agents associated with municipal wastewater and sludge are those found in thedomestic sanitary waste of the population and from industries that process meats, fish, and other food products.These microbial pathogens include a large number of bacteria, viruses, and parasites. Important examples aremembers of the bacterial genera Salmonella and Shigella; the infectious hepatitis, Rota and Norwalk viruses; andthe parasites associated with giardiasis, cryptosporidiosis, taeniasis, and ascariasis (See Table 5.1 for a morecomplete list). It is reasonable to assume that any or all of these infectious agents might be present in the water andsolids fractions of raw sewage.

INFECTIOUS DISEASE TRANSMISSION

Three conditions are necessary to produce infectious disease in a population: (1) the disease agent must bepresent, (2) it must be present in sufficient concentration to be infectious, and (3) susceptible individuals mustcome into contact with the agent in a manner that causes infection and disease. From a public health perspective, itis prudent to presume that raw sewage and sludge contain pathogenic organisms; thus, the first of the abovecriteria is always met. The concentration of these agents in sewage will be a function of the disease morbidity inthe contributing population. An example of the number of pathogenic microorganisms found in raw sewage,treated effluent, and in raw and treated sludge is shown in Table 5.2.

The second of the above criteria—that the infectious agent be present in sufficient concentration—is fraughtwith uncertainty because available data on human dose response are very limited, particularly at the populationlevel. Usually it takes more than a single organism to produce a detectable disease response in an individual in theexposed population. In many instances a lower dose of pathogens will produce infection but not disease. Thelimited human dose-response data that have been reported indicate much variation in the severity of sicknessamong those exposed to known dosages of pathogens (Bryan, 1974). Table 5.3 contains some examples ofbacterial pathogen dose response.

PUBLIC HEALTH CONCERNS ABOUT INFECTIOUS DISEASE AGENTS 89

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TABLE 5.1 Examples of Pathogens Associated With Raw Domestic Sewage and Sewage Solids

Pathogen Class Examples Disease

Bacteria Shigella sp. Bacillary dysentery

Salmonella sp. Salmonellosis (gastroenteritis)

Salmonella typhi Typhoid fever

Vibrio cholerae Cholera

Enteropathogenic-Escherichia coli A variety of gastroenteric diseases

Yersinia sp. Yersiniosis (gastroenteritis)

Campylobacter jejuni Campylobacteriosis (gastroenteritis)

Viruses Hepatitis A virus Infectious hepatitis

Norwalk viruses Acute gastroenteritis

Rotaviruses Acute gastroenteritis

Polioviruses Poliomyelitis

Coxsackie viruses ''flu-like" symptoms

Echoviruses "flu-like" symptoms

Protozoa Entamoeba histolytica Amebiasis (amoebic dysentery)

Giardia lamblia Giardiasis (gastroenteritis)

Cryptosporidium sp. Cryptosporidiosis (gastroenteritis)

Balantidium coli Balantidiasis (gastroenteritis)

Helminths Ascaris sp. Ascariasis (roundworm infection)

Taenia sp. Taeniasis (tapeworm infection)

Necator americanus Ancylostomiasis (hookworm infection)

Trichuris trichuria Trichuriasis (whipworm infection)

The final link in the infectious disease transmission chain is the exposure of the susceptible human populationto infectious agents. The primary route of exposure to wastewater-associated pathogens is by ingestion, althoughother routes, such as respiratory and ocular, can be involved. If reclaimed water and sludges are to be used in theproduction of human food crops, particularly those that are eaten raw, then there is a chance of exposure throughingestion. Consequently, there is a greater need to reduce pathogen numbers to low levels prior to soil application,or at least prior to crop harvesting or livestock exposure.

Available engineering knowledge and technology can produce reclaimed water of the desired quality for usein such activities as agriculture, landscape irrigation, and ground water recharge. Data in Table 5.2 are illustrativeof the effect of tertiary (advanced) treatment of wastewater in the removal of pathogens. The technology hasadvanced such that, in a number of instances, the use of reclaimed water to augment of water sources for drinkingwater supplies is either being seriously proposed or is a reality (City of San Diego, 1992; Gunn and Reberger,1980; James M. Montgomery, Inc., 1983; Lauer and Johns, 1990). Treatment processes are also available toeffectively reduce the concentration of pathogens in sewage sludge to levels safe for direct contact. Someexamples include lime treatment, heat treatment, drying and composting (EPA, 1992b).


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TABLE 5.2 Typical Numbers of Microorganisms Found in Various Stages of Wastewater and Sludge Treatment

Number Per 100 ml Of Effluent Numbers Per Gram of Sludge

Microbe Raw Sewage PrimaryTreatment

SecondaryTreatment

Tertiarya

TreatmentRaw Digestedb

Fecal coliformMPNc

1,000,000,000 10,000,000 1,000,000 <2 10,000,000 1,000,000

SalmonellaMPN

8,000 800 8 <2 1,800 18

Shigella MPN 1,000 100 1 <2 220 3

Enteric virusPFUd

50,000 15,000 1,500 0.002 1,400 210

Helminth ova 800 80 0.08 <0.08 30 10

Giardialamblia cysts

10,000 5,000 2,500 3 140 43

a Includes coagulation, sedimentation, filtration and disinfectionb Mesophilic anaerobic digestion.c MPN = Most Probable Numberd PFU = Plaque-forming unitsSOURCES: EPA, 1991 and 1992a; Dean and Smith, 1973; Feachem et al., 1980; Engineering Science, 1987; Gerba, 1983 and Logsdon et al.,1985.

Thus, the technical knowledge is available for the design of processes that can adequately reduce the numberof infectious agents present in raw wastewater and solids to safe levels. The important public health concern lies inthe ability of these processes to reliably produce an acceptable product. Such reliability must be a critical elementin the design and operation of wastewater treatment plants or other facilities producing these materials.

In California, treatment processes specified by the Water Reclamation Criteria (California Water Code, 1994)can achieve a 5 orders of magnitude reduction in situ of viruses. This level of reduction produces effluent that isaccepted as being "free" of viruses. In the Monterey Wastewater Reclamation Study for Agriculture (Sheikh et al.,1990), tests conducted over a 5-year period of over 80,000 gal of reclaimed water that met Title 22 requirementsfound no viruses (Engineering Science, 1987). Virus seeding studies were conducted that verified the 5-logreduction in viruses from the treatment process. Additionally, a 99 percent natural die-off rate over 5 days wasdemonstrated under both field and laboratory conditions for the virus T99.

A rough calculation illustrates the very low level of viruses to be expected after irrigation with reclaimedwater of this quality on food crops. In the Monterey study, the median number of viruses detected in the rawwastewater influent was 8 plaque-forming units (pfu) in 67 samples, so that even without treatment, the number ofviruses that might remain following irrigation is very small. To illustrate, reclaimed water is typically applied tothe crop in an


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TABLE 5.3 Dose Required for a 25 to 75 Percent Disease Response in Humans

Number of Bacteria Bacterial Species

100 – 1,000 Shigella sp.

1,000 – 10,000,000 Salmonella typhi (Typhoid fever)

100,000 – 1,000,000,000 Salmonella sp. (Gastroenteritis)

1,000 – 100,000,000 Vibrio cholerae (Cholera)

SOURCE: Bryan, 1974.

"irrigation set" of 2 in. of water. In California, crops cannot be harvested for two weeks following a reclaimedwater irrigation set. If a plant occupies 2 square feet, it would receive about 2.4 gal of water. Even if the treatmentplant failed completely, and assuming all the viruses in that volume of untreated wastewater stuck to the ediblepart of the plant, one would expect approximately 10-3 pfu per plant. With treatment, the number of virusesremaining on the plant is essentially zero. The study also found that a five-log reduction in viruses occurred in soilafter ten days.

While the use of essentially pathogen-free sewage sludge or effluent would be ideal, materials of lessersanitary quality (less treatment) can be applied in cases where direct human exposure to applied sludge or effluentis minimal. In these instances natural decay processes in the soil would be relied on to reduce the number ofpathogenic agents to safe levels. Site restrictions would be required to limit public access and to allow adequatetime for pathogen reduction prior to crop planting, harvesting, or domestic animal grazing.

INFECTIOUS DISEASE RISK

Where wastewater or sludge treatment is the primary mechanism to protect the public from infectiousdisease, acceptable microbiological quality standards must be developed. In the case of treated effluents used forcrop irrigation, these values have developed over time and are based upon the use of standard water qualitybacterial indicator microorganisms (e.g., coliform group or fecal coliform bacteria). More recently, specifictreatment processes have been relied on to effect a significant reduction in the numbers of viruses and parasites(i.e. a process standard rather than a strict microbiological standard). For example, the Water Reclamation Criteriaof California, which has been a model of reclaimed water regulations for many states (see Chapter 7), hasestablished process standards for crop irrigation to ensure that the reclaimed water has a concentration of totalcoliform (or fecal coliform) less than or equal to 2.2 per 100 ml. This criteria is considered safe for humancontact, and is based on past experience of health professionals and on a lack of detectable health problemsassociated with agricultural irrigation with treated effluent that meet this microbiological quality criteria. Thus, themicrobiological quality values are not based on a formal risk assessment but rather on experience and theknowledge


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that accepted treatment processes can effectively reduce pathogen numbers.There is, in the United States, less public health experience with sludge application than there is with

wastewater reuse. EPA has established microbial quality criteria for sewage sludge that is to be applied to land inthe Part 503 Sludge Rule (EPA, 1993). As with reclaimed water, the microbiological standards for sludge in thePart 503 Sludge Rule (discussed in more detail in Chapter 7) are also set primarily on the basis of experience, andexpected efficiency of treatment processes to reduce pathogens.

There is a desire among regulators, producers, and users to develop and evaluate standards based on a moredefined framework for risk assessment. This desire is generating interest in the use of mathematical models topredict the risk of infectious disease among those exposed to domestic waste-associated materials. Mathematicalmodeling makes assumptions explicit and is useful in organizing data and assumptions into a framework that leadsto quantitative predictions. Models should, however, be used with caution. The model itself brings no new data orinformation to the process, and careful interpretation of modeling results is required; a numerical result of a modelhas human health significance only in the context of the model's assumptions. The mathematical format andnumerical output of these models can lead to overconfidence in their results. There is the danger that inaccurateparameter estimates can lead to unrealistic risk forecasts.

Attempts to provide a quantitative model for the assessment of human health risks associated with theingestion of waterborne pathogens have generally focused on estimating the probability of an individual infectionresulting from a single exposure event. Most models described in the literature are of the same generic form(Fuhs, 1975; Dudley et al., 1976; Hass, 1983; Payment, 1984; Asano and Sakaji, 1990 and Rose and Gerba,1991). They give a single value estimate of the probability of a particular exposure leading to infection or diseasein a single individual and, except for Dudley's work, provide little or no information on the uncertainty orvariability in this estimate.

A different approach to infectious disease risk assessment modeling starts from a population perspective andcarries the analysis beyond the simple individual risk of infection or disease by estimating the probabilitydistribution of the number of infected or diseased people in the exposed population (Cooper et al., 1986; Olivieriet al., 1986, 1989). This type of dynamic model allows for the evaluation of the sensitivity of the risk distributionto varying the dose and to varying the dose-response assumptions. Ideally the dynamic risk model should includethe size of the exposed population, the immune status of the population, and other relevant demographic factors.The strength of this modeling approach is that it overtly acknowledges both uncertainty and variability inparameter values in a structured fashion that helps avoid unrealistic worst-case analysis results. Presently, it wouldbe premature to give too much weight to the results of any of the existing models. It is anticipated that thedevelopment of the more sophisticated dynamic models will eventually enable risk managers to better understandthe uncertainties involved and more realistically evaluate risk estimates.

MONITORING INFECTIOUS DISEASE POTENTIAL

Many of the variables associated with the transmission of infectious disease from wastewater


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and sludge are either not well understood or are unpredictable. Thus, it is essential that the dose of infectiousagents in these materials be reduced to numbers that minimize the risk of disease transmission. This implies that atreatment process, including site restrictions, be applied that will reliably reduce the concentration of pathogens toan acceptable level prior to human or animal contact.

There is a great diversity of pathogenic agents involved in the fecal-oral exposure route, and an equaldiversity of dose-response relationships. Monitoring for all of these agents is impractical; therefore, the use ofindicator organisms has been the traditional approach to estimating sanitary quality. Coliform bacteria have beenthe most used in this regard. Their presence in the environment, particularly the fecal coliforms, is an indication ofthe presence of animal and human fecal matter, and thus the possible presence of many associated pathogens.Intestinal bacterial pathogens will react to environmental phenomena in much the same manner as coliforms, sothe rates of removal of coliforms during water reclamation or sludge processing should reflect a similar reductionin pathogenic bacteria. Coliform bacteria determinations, in themselves, may not adequately predict the presenceof viruses, protozoa or helminths. Many enteric viruses, for example, have a greater resistance to chemicaldisinfection and irradiation than do most bacterial indicators.

There are instances in sludge processing, such as composting, in which the coliform levels cannot besatisfactorily reduced even though there is reason to believe that the sanitary quality of the material is otherwiseacceptable (EPA, 1992b; Skanavis and Yanko, 1994). In this situation, when the coliform numbers remain high,one should directly monitor for species of Salmonella to demonstrate the absence of this common bacterialpathogen.

Many of the parasites of concern exist in the encysted stage outside of the human or animal intestinal track,and are quite resistant to chemical and physical disinfection in this form. Wastewater reclamation practice relies onthe treatment process to control these parasites. Parasite ova and cysts concentrate in sewage sludge and thus areof most concern for land application of sludge. Helminth ova are very resistant to those environmental factors thatreduce the numbers of bacterial indicators or animal viruses in sludge. Because of its particular resistance, thepresence or absence of viable helminth ova is being used as a criterion for monitoring for the presence ofhelminths in sludge to be applied to land (EPA, 1993).

As previously explained, there in no general agreement on the numerical values used in settingmicrobiological standards. They vary from region to region, both domestically and internationally. The standardsare based on expected performance of wastewater treatment processes and on past experience with land applicationrather than on predictive science.

Because coliform bacteria are not always reliable indicators of the sanitary quality of reclaimed water or ofsludge, there is a continuing search for substitute indicator organisms or for methods for directly measuringpathogens. The bacterium Clostridium perfringens is an example. Because of its presence in large numbers inwastewater, ease and speed of detection and the resistance of its spores to disinfection, this bacterium is consideredby some to be a good indicator of how effective a treatment process has been. The evaluation of such potentialprocess monitoring indicators should be encouraged.

Applications of immunological and molecular biological methods to environmental microbiology areevolving and offer the possibility for low levels of pathogenic microbes to be detected directly fromenvironmental materials such as water and soil. Fluorescent antibody


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(FA) methods are available that are both qualitative and quantitative for specific microbial pathogens such asGiardia and Cryptosporidium . Gene probes have equal or greater specificity for species of microorganisms asFA, but at the present time are less suitable for rapid quantification. The application of polymerase chain reaction(PCR) methodology has the potential to detect very low levels of specific pathogen nucleic acid and, by inference,the presence of pathogenic microbes. While the application of these sensitive detection methods could result inmore definitive monitoring, questions remain about the viability of the microbes detected and about the publichealth significance detecting very low numbers of these agents in water and sludge that are applied to land.

PUBLIC HEALTH EXPERIENCE WITH THE USE OF RECLAIMED WATER AND SLUDGE

There is an extensive literature on the public health (infectious disease) experience with wastewaterreclamation and reuse (EPA, 1992a). This is not the case for the application of treated sludge onto land. Therehave been no reported outbreaks of infectious disease associated with a population's exposure—either directly orthrough food consumption pathways—to adequately treated and properly distributed reclaimed water or sludgeapplied to agricultural land.

Reports of the occurrence of infectious disease transmission linked to the irrigation of food crops withwastewater are associated with untreated sewage or treated wastewater of questionable quality. A recentepidemiological review of disease transmission from irrigation with reclaimed water (Shuval, 1990) alsoconcludes that only untreated wastewater has been implicated in the transmission of infectious disease. Except forthe use of raw sewage or primary effluent on sewage farms in the late 19th century, there have not been anydocumented cases of infectious disease resulting from reclaimed water use in the United States (EPA, 1992a,Water Pollution Control Federation, 1989).

In California, as a result of the Monterey study and others (Sheikh et al., 1990), a treatment process forreclaimed water has been approved by the state for any nonpotable purpose, including application to crops eatenraw. State health officials are convinced that specific treatment processes can be used to reduce the levels ofpathogens such that treated wastewater is "safe to use." California standards for reclaimed water tend to lead theway in the United States, and are compatible with those developed by EPA in their Guidelines for Water Reuse (EPA, 1992a). See Chapter 7 for a discussion of the regulations governing pathogen control in reclaimed water andsludge.

The most extensive literature on human exposure to wastewater is concerned with the infectious disease riskto wastewater treatment plant operators and maintenance personnel. A review of the literature indicates that theoccurrence of clinical disease associated with occupational exposure among these workers is rarely reported(Cooper, 1991a,b). From these observations it is not unreasonable to assume that exposure of agricultural workersto reclaimed water used in irrigation would result in an even lower risk of infectious disease than that to sewageplant operators.

Because of the intense public concern over AIDS, sewage treatment plant operators and others who come inclose contact with wastewater and sludges have questioned their risk of


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infection with the HIV virus. All evidence indicates that there is no cause for alarm since the HIV virus does notsurvive in water; its transmission requires intimate contact with infected blood or body fluids (Moore, 1993;Riggs, 1989).

There have been a limited number of reports concerning an allergic response in sewage treatment plantworkers exposed to species of Aspergillus fungi in the dust associated with the composting of sewage sludge(Clark et al., 1984; Epstein, 1994). In this instance the fungi source is not wastewater but growth of this commonfungi as part of the composting process.

The potential effects of aerosols generated by wastewater treatment plants on the surrounding communityhave been the subject of much speculation. To date, the information collected by multiple investigators indicatesthat no health problems have been demonstrated to be associated with these aerosols. This issue was thoroughlydocumented in the proceedings of an EPA symposium on wastewater aerosols and disease (Pharen, 1979). Fromthese observations, one could assume that the risk of contracting infectious disease from exposure to aerosols ofreclaimed irrigation water is also negligible. No adverse health effects have ever been reported from the irrigationof median strips, parks, or private residences irrigated with properly treated reclaimed wastewater.

The limited number of epidemiological studies that have been conducted in the United States on treatmentplant workers exposed to municipal wastewater or sludge or populations exposed to reclaimed water or treatedsludge land application projects indicate that exposure to these materials was not a significant risk factor.However, the value of prospective epidemiological studies on reclaimed water or sludge use is limited because of anumber of factors, including a low illness rate—if any—documented as resulting from these reuse practices,insufficient sensitivity of current epidemiological techniques to detect low-level disease transmission, populationmobility, and difficulty in assessing actual levels of exposure.

Infectious diseases of the types that could be associated with municipal wastewater are under-reported andexposures are scattered, so that effects may well go unrecorded. From a public health point of view, the majormicrobiological considerations for evaluating any reuse management scheme are the ability to effectively monitorfor treatment efficacy and the reliability of the process used to effect pathogen reduction.

One must keep in mind that there are a great many sources of these infectious disease agents other than reuseof wastewater or sludge, such as prepared food and person-to-person contact. Therefore, the potential addedincrement of pathogen exposure from the proper reuse of reclaimed water or sludge is minuscule compared to oureveryday exposure to pathogens from other sources.

SUMMARY

Pathogenic microbes are inherent to domestic sewage and sewage solids. Because of the potential for thetransmission of these infectious disease agents to humans and animals, use of these effluents on crops and grazingland must employ management strategies that protect the public's health. The main thrust of any managementstrategy is reduction of concentrations of pathogens to acceptable levels. This reduction can be achieved bytreatment prior to land application or, as an alternative scheme in the case of sludge and reclaimed water of lower


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sanitary quality, crop restrictions and management of the application site to restrict human and grazing animalcontact during the time required for pathogens to decay to acceptable levels. Two prime considerations inevaluating any management scheme are the ability to effectively monitor for treatment efficacy and the reliabilityof the process used to effect pathogen reduction.

REFERENCES

Asano, T., and Sakaji, R. H. 1990. Virus risk analysis in wastewater reclamation and reuse. P. 483 in Chemical Water and WastewaterTreatment. Hahn and Klute eds. Heidelberg: Springer-Verlag.

Bryan, F. L. 1974. Diseases transmitted in food contaminated with wastewater. EPA 660/2-74-041, June 1974. Washington, D.C.: U.S.Environmental Protection Agency.

California Water Code. 1994. Porter-Cologne Water Quality Control Act . California Water Code, Division 7. Compiled by the State WaterResource Control Board, Sacramento, Calif.

City of San Diego. 1992. Total Resource Recovery Project: Health Effects Study. Final Summary Report prepared by the Western Consortiumfor Public health, San Diego, Calif.

Clark, C. S., J. Bjornson, J. W. Schwartz-Fulton, J. W. Holland, and P. S. Gatside. 1984. Biological health risks associated with composting ofwastewater treatment plant Sludge. Jour. WPCF 56: 1269.

Cooper, R. C., A. O. Olivieri, R. E. Danielson, P. G. Badger, R. C. Spear, and S. Selvin. 1986. Evaluation of Military Field-Water Quality.Vol. 5. Infectious Organisms of Military Concern Associated With Consumption: Assessment of Health Risks and Recommendationsfor Establishing Related Standards, UCRL-21008. Lawrence Livermore National Laboratory, Livermore, Calif.

Cooper, R. C. 1991a. Public health concerns in wastewater reuse. Water Sci. Technol. 24(9):55.———. 1991b. Disease risk among sewage plant operators: a review. Sanitary Engineering and Environmental Health Research Laboratory

Report No. 91-1. Berkeley: University of California.Dean, R. S., and J. E. Smith. 1973. The Properties of Sludges. Pp 39–47 in Proc. of the Joint Conference On Recycling Municipal Sludges And

Effluents On Land. July, 1973 Champaign, Ill. National Association of State Land-Grant Colleges, Washington, D.C.Dudley, R. H., K. K. Hekimian, and B.J. Mechalas. 1976. A scientific basis for determining recreational water quality criteria. Jour. WPCF 48

(12):2761-2777.Engineering Science, Inc. 1987. Monterey wastewater reclamation study for agriculture—final report, April 1987. Berkeley, California:

Engineering Science, Inc.EPA. 1991. Preliminary Risk Assessment For Parasites In Municipal Sewage Sludge Applied To Land. EPA 600/6-91/001. March 1991.

Washington, D.C.: U.S. Environmental Protection Agency.


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form

attin

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———. 1992. Technical support document for reduction of pathogens and vector attraction in sewage sludge. EPA R-93-004. Washington,D.C.: U.S. Environmental Protection Agency.

———. 1992a. Manual Guidelines for Water Reuse. EPA 625/R-92/004. Washington, D.C.: U.S. Environmental Protection Agency.———. 1993. Standards for the Use or Disposal of Sewage Sludge; Final Rules, 40 CFR Parts 257, 403, and 503. Federal Register 58(32):

9248-9415.Epstein, E. 1994. Design and operations of composting facilities: Public health aspects. Pp. 1–23 in The Management of Water And

Wastewater Solids For The 21st Century. Proceedings of WEF Specialty Conference, June 1994. Water Environment Federation,Alexandria, Vir.

Feachem, R. G., D. L. Bradley, H. Garelick, and D. D. Mara. 1980. Technology for Water Supply and Sanitation—Health Aspects of Excretaand Sullage Management: A State of the Art Review. Washington, D.C.: The World Bank.

Fuhs, G. W. 1975. A Probabilistic Model of Bathing Beach Safety. Science of The Total Environment 4:165.Gerba, C. P. 1983. Pathogens. Pp 147–195 in Utilization of Municipal Wastewater and Sludge on Land. A. L. Page, T. L. Gleason, J. E. Smith,

I. K. Iskander, and L. E. Sommers, eds. Riverside: University of California.Gunn, G. A., and G. W. Reberger. 1980. Operator training and plant start-up for a regional water reclamation project. Jour. WPCF 52(9):235.Hass, C. N. 1983. Effect of effluent disinfection on risks of viral disease transmission via recreation water exposure. Jour. WPCF 55(8).James M. Montgomery, Inc. 1983. Operation, Maintenance and Performance Evaluation of the Potomac Estuary Experimental Water

Treatment Plant. Executive Summary. Sept 1980–1983. James M. Montgomery, Inc., Pasadena, Calif.Lauer, W. C., and F. J. Johns. 1990. Comprehensive health effects testing program for Denver's potable water reuse demonstration project.

Jour. Tox. and Environ. Health 30: 305.Logsdon, G.S., V. C. Thurman, E. S. Frindt, and J. G. Stoeker. 1985. Evaluating sedimentation and various filter media for the removal of

Giardia cysts. Jour. AWWA 77(2):61.Moore, E. M. 1993. Survival of human immunodeficiency virus (HIV), HIV-infected lymphocytes and poliovirus in water. App. Environ.

Microbiol. 59(9): 1437Olivieri, A. W., R. C. Cooper, R. C. Spear, S. Selvin, R. E. Danielson, D. E. Book, and P. G. Badger. 1986. Risk Assessment of Waterborne

Infectious Agents. P. 287 in Proc. Envirosoft 86, International Conference On Development and Application of Computer Techniquesto Environmental Science. Boston: Computational Mechanics Publ.

Olivieri, A. W., R. C. Cooper, and R. E. Danielson. 1989. Risk of waterborne illness associated with diving in the Point Loma kelp beds, SanDiego, Calif. Proc. ASCE 1989 Specialty Conference on Environmental Engineering, Austin, Texas. American Society of CivilEngineers, Boston, Mass.

Payment, P. 1984. Viruses and bathing beach quality. Canadian Jour. of Public Health 75:43


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Pharen, H. 1979. Wastewater aerosols and disease assessment. Proc. Symposium on Wastewater Aerosols and Disease. EPA 1-79-019.Washington, D.C.: U.S. Environmental Protection Agency.

Riggs, J. L. 1989. AIDS transmission in drinking water: no threat. Jour. AWWA 81(9): 69.Rose, J. B., and C. P. Gerba. 1991. Use of risk assessment for the development of microbial standards. Water Sci. Technol. 24(2):29.Sheikh, B., R. Cort, W. Kirkpatrick, R. Jaques, and T. Asano. 1990. Monterey wastewater reclamation study for agriculture. Journ. WPCF 62

(3):216–226.Shuval, H.I. 1990. Wastewater irrigation in developing countries: health and technical solutions. Summary of World Bank Technical Report.

51. Washington, D.C.: World Bank.Skanavis, C., and W. A. Yanko. 1994. Evaluation of composted sewage sludge-based soil amendments for potential risks of salmonellosis.

Jour. of Environ. Health 56(7):19.Water Pollution Control Federation, 1989. Water Reuse. 2nd Edition. Manual of Practice SM-3. Alexandria, Vir.: Water Environment

Federation.


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6

Public Health Concerns About Chemical Constituents inTreated Wastewater and Sludge

There are many chemical constituents that enter the municipal waste stream that are of potential concern forhuman health. These substances include organic chemicals, inorganic trace elements (such as cadmium and lead),and nitrogen. Conventional agricultural practices, such as the use of commercial fertilizers, also have the potentialto introduce additional chemical constituents to soil. However, this report is not attempting a comparison betweenpublic health effects of conventional agricultural inputs and those derived from municipal wastewater or sludge.The degree to which constituents from municipal wastewater present a risk to human health depend on theirconcentration in reclaimed water and treated sludge and the fate and transfer of these chemicals from thewastewater/sludge sources to human receptors via various exposure pathways. The chemical composition ofsewage and the degree to which chemical concentrations are reduced in effluent and sludge by secondary andadvanced treatment were discussed in Chapter 2 and 3. The degree to which chemical concentrations of thesecontaminants in reclaimed wastewater and sludge are further reduced through natural processes in theenvironment and their availability to food plants were the subjects of Chapter 4. Transmission of toxiccontaminants to humans from agricultural use of reclaimed wastewater and sludge is covered in this chapter.

The U.S. Environmental Protection Agency (EPA) identified Priority Pollutants in regulations that deal withmunicipal and industrial wastewater (EPA, 1984) due to their toxicity to humans and the aquatic environment.These Priority Pollutants are divided into four classes: (1) heavy metals (oftentimes referred to as trace elementsor trace metals) and cyanide, (2) volatile organic compounds, (3) semivolatile organic compounds, and (4)pesticides and polychlorinated biphenyls (PCBs). In addition, nontoxic organic compounds in wastewater can betransformed into potentially toxic chlorinated organic compounds, such as trihalomethanes, when chlorine is usedfor disinfection purposes (National Research Council, 1980).

For the purpose of this review, non-metallic trace elements, such as selenium, are grouped together with theheavy metals under the more general designation of ''trace elements." The following discussion first considers thefate of organic compounds from sludge and wastewater applications to soil. The uptake of these chemicals intoplants and animals that go into the human food chain is then examined. Finally, the potential for adverse healtheffects from trace elements in sludge and wastewater via these same pathways is evaluated.

PUBLIC HEALTH CONCERNS ABOUT CHEMICAL CONSTITUENTS IN TREATED WASTEWATER AND SLUDGE 100

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FATE OF AND EXPOSURE TO ORGANIC CHEMICALS

Principal pathways of human exposure to sludge- and effluent-borne toxic organic compounds from landapplication to cropland include (Dean and Suess, 1985):

• Uptake by plant roots, transfer to edible portions of plants, and consumption by humans.Direct contact of edible plant parts with sludge or reclaimed water applied by spraying, and

consequent consumption by humans.• Direct contact by children who play on sludge/wastewater-treated soil and inadvertently ingest small

amounts of soil.• Uptake by plants used as animal feed, animal ingestion causing transfer to animal food products, and

consumption of the animal food products by humans.• Direct ingestion of soil and/or sludge by grazing animals, transfer to animal food products, and

consumption of animal food products by humans.

Human exposure to toxic organic chemicals through incidental ingestion of sludge, effluents, or treated soil(pathways 2 and 3 above) is not considered in detail in this report. Chapter 7 discusses EPA's risk analysis, whichevaluated all exposure pathways.

Behavior of Toxic Organics in the Soil

It has been suggested that most toxic organic compounds are present in sludge at concentrations less than 10.0mg/kg (Jacobs et al., 1987). Therefore, when sludges are applied to soil at agronomic rates and mixed with thesurface, concentrations of toxic organics within the top 15 cm of soil normally will not exceed 0.10 mg/kg. In onesurvey, the level of toxic organics in sludge-amended soils was considered to be similar to or lower thanbackground pesticide soil concentrations of 0.01 to 1.0 mg/kg (Naylor and Loehr 1982). They are further reducedby microbial decomposition.

In theory, there are a number of environmental processes that, when added to the soil, can interrupt the entryof toxic organic chemicals into the food chain. Organic chemicals from wastewater or sewage sludge may bedestroyed directly after land application by biodegradation and chemical- and photo-oxidation. Organiccompounds may also be volatilized, immobilized onto solid particles by sorption processes, or transported(leached) unaltered through the soil column to reach the ground water. In more complex mechanisms, sorbedorganics may subsequently be chemically or photochemically degraded, microbially decomposed, or desorbed.

A considerable body of research has been performed on the behavior of organic pesticides in soil. Bothlaboratory and field experiments suggest that during land treatment, most pesticide residues are adsorbed by soilparticles and remain sorbed on surface soils until degraded by microorganisms or volatized (Cork and Krueger,1991). The relative degree of intrinsic biodegradability of toxic organics on the EPA Priority Pollutants list wasillustrated by Tabak et al. (1981) in laboratory studies. They collected data on biodegradability and microbialacclimation of 96 compounds using bacterial inoculum from domestic wastewater and synthetic


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bacterial growth medium. Their overall results are summarized in Table 6.1. Significant biodegradation was foundfor phenolic compounds, phthalate esters, naphthalenes, and nitrogenous organics; variable results were found formonocyclic and polycyclic aromatic compounds, PCBs, halogenated ethers, and halogenated aliphatics; and nosignificant biodegradation was found for organochlorine pesticides.

Extrapolation of laboratory findings like these to predicting behavior in the field has two importantconstraints: (1) the rate of biodegradation in soil is probably less than that in laboratory medium and (2) the lowconcentration of the organics in reclaimed wastewater applied to crops may not support the level of microbialactivity necessary for biodegradation in the soil environment.

Literature on the microbial decomposition of toxic organics in soil is diverse (Alexander, 1994). Thedegradation of petroleum hydrocarbons (a mixture of aliphatic, aromatic, and asphaltic compounds) in soils hasbeen reviewed by Atlas (1981). Factors which appear to be important in encouraging high decomposition rates ofpetroleum hydrocarbons are temperature, concentrations, adequate supply of essential nutrients, and availability ofoxygen. There is little evidence for significant leaching of petroleum organic compounds from the upper soillayers. Experiments with the high-rate application of sludge containing high levels of petroleum hydrocarbons ontoland have shown a 77 percent degradation rate near the surface after one year, with most of the degradedcompounds being n-alkanes (Lin, 1980). It was concluded that sludge land disposal would not result in petroleumhydrocarbon buildup in the soil. Also, in studies of other organic substances in wastewaters used for irrigation,Dodolina et al. (1976) found that acetaldehyde, crotonaldehyde, benzaldehyde, cyclohexanone, cyclohexanol, anddichloroethane disappeared from soil within ten days.

The behavior of PCBs in soil has been comprehensively reviewed by Griffin and Chian (1980), whoconcluded that PCBs are strongly adsorbed by soil particulates. Influential factors affecting adsorption are thenature of the soil surface, the soil organic matter content, and the chlorine content and/or hydrophobicity of theindividual PCB isomers. Adsorption increases with increasing organic matter content of the soil, with increasingchlorine content, and with increasing hydrophobicity of the PCB molecules. One study that examined percolationof PCB-containing solution through soil columns showed that less than 0.05 percent of one isomer was leached inthe worst case. Fairbanks and O'Connor (1984) have shown that PCBs remain tightly adsorbed to sludge-amendedsoil, with minimal transport by soil water.

Studies involving land treatment of municipal wastewater provide some insight into the fate of toxic organiccompounds from wastewater in soils. Land treatment of wastewater is considered to be an alternative form ofsecondary treatment, and is not performed for crop irrigation purposes. Generally, land treatment systems applysettled wastewater (primary effluent) to vegetated slopes using sprinklers or perforated pipes. The water flowsover the sloped surface to collection ditches at the bottom of the slope where the effluent is discharged to a surfacewater. Biodegradable organic compounds, such as organic nitrogen and ammonia, are oxidized by soil bacteria.Percolation into the soil is negligible. Overland flow treatment slopes are selected for their relativeimpermeability; also, particulate material tends to seal the soil rapidly. Some water evaporates, but most of thewastewater is collected as surface runoff (Metcalf and Eddy, 1991). Wastewater flows in a very thin sheet acrossthe vegetated slope. The U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory inNew


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TABLE 6.1 Biodegradability of Priority Pollutant Organic Compounds

Test Compound Class Number of compounds tested Percent Degradationa

Phenols 11 82 D

Phthalate Esters 6 67 D

Naphthalenes 4 100 D

Monocyclic Aromatics 12 42 D, 50 T

Polycyclic Aromatics 7 50 A, 50 N

Polychlorinated Biphenyls (PCBs) 7 71 N

Halogenated Ethers 6 50 N, 50 D

Nitrogenous Organics 6 67 D, 33 N

Halogenated Aliphatics 23 26 D, 57 A or B, 17 C or N

Organochlorine Pesticides 17 100 N

a D-Significant degradation with rapid adaptation; A-significant degradation with gradual adaptation; T-significant degradation withgradual adaptation followed by a deadaptive process (toxicity); B-slow to moderate biodegradative activity, concomitant with significantrate of volatilization; C-very slow biodegradative activity, with long adaptation period needed; N-not significantly degraded under theconditions of test method.SOURCE: Condensed from Tabak et al., 1981.

Hampshire operated a prototype overland flow wastewater land treatment system and found greater than 94percent removal of each of 13 trace organics by volatilization and adsorption processes (Jenkins et al. 1983), withremoval efficiencies decreasing as application rates increased and temperature decreased. With the possibleexception of PCBs, biodegradation prevented contaminant buildup in the surface soil.

Uptake of Toxic Organics by Plants

The following discussion summarizes information presented by O'Connor et al. (1991) from a recent reviewof the literature dealing with plant uptake of toxic organics. The results reported in the O'Connor et al. review are amixture of laboratory and field data on plant uptake of organic compounds, both from sludge and from additionsof pure chemical.

Phthalate Esters

Phthalate esters, which are the most common toxic organic compounds in sludges, present little risk becauseplants serve as effective detoxifying barriers to these chemicals and prevent their accumulation in the food chain(Aranda et al. 1989). Also, phthalates added to soils do not persist and are rapidly removed by volatilization andmicrobial decomposition (Dorney et


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al., 1985).

Polynuclear Aromatic Hydrocarbons (PAHs),

PAHs (also called "polycyclic aromatics") are produced by incomplete combustion. They are among the mostcommon toxic organics in sludges (EPA, 1990). In the National Sewage Sludge Survey (NSSS), the PAH benzo(a)pyrene was found just at detection levels in 3 percent of the sludges analyzed from 209 municipal treatmentplants. An earlier sludge survey of 40 municipal treatment plants conducted in the late 1970s by the EPA (EPA,1982) found benzo(a)pyrene in 21 percent of the sludges with a mean level of 0.1 mg/kg (Kuchenrither and Carr,1991). Some PAHs, particularly higher molecular weight species, are long-lived in soils (Bossert and Bartha,1986). However, in long-term field studies (20-30 yrs), no evidence was found of elevated PAH concentrations inthe above-ground portions of several crop species grown in PAH-contaminated soils. Air-borne sources of PAHswere regarded as the main origin of plant contamination in sludge-amended and control treatments alike (Witte etal., 1988; Kampe 1989; Wild et al., 1990). Overall, O'Connor et al. (1991) concluded that minimal PAHcontamination occurred when sludge was used prudently for agriculture. The transfer of PAHs from soil wasminimal for root crops, and essentially zero for above-ground crops.

Polychlorinated Biphenyls (PCBs).

Two studies found the median total PCB content in municipal sludges to be less than 0.5 mg/kg total PCBs(Jacobs et al. 1987; Mumma et al. 1988). The NSSS confirms this finding (EPA, 1990); it was found in the surveythat the median concentration was 0.2 mg/kg. More highly chlorinated PCB cogeners, which dominate inmunicipal sludges, tend to be more persistent, more strongly sorbed, less volatile and less bioavailable than theless chlorinated PCB species. O'Connor et al. (1990) conducted field studies and greenhouse pot studies usingsludge-borne PCBs and found that the PCB levels in crops were below Limits of Detection (LOD), typically 0.20µg/kg; bioconcentration factors were usually less than 0.02 based on dry weights of soil and crop and LOD. Therewas no statistically significant evidence of PCB uptake from sludge-borne PCBs in soils by aboveground parts ofplants. Carrots were the only crop to contain detectable residues of PCBs, mostly in the carrot peel, which theauthors noted can be easily removed with normal culinary practices of washing and peeling. No PCB vaporcontamination of crops grown in soils amended with sludge-borne PCBs was detected.

Surface incorporation of PCB-contaminated sludges reduces PCB volatilization (Strek et al. 1981). Lowinputs of PCBs to soil-plant systems, combined with low bioavailability, suggest negligible impact on plantsgrown in sludge-amended soils (Webber et al., 1994; O'Connor et al., 1991; Chaney, 1993). Witte et al. (1988)reported that repeated applications of municipal sludge over a period of 30 years and totaling 130 metric tons perha, resulted in slight increases in soil PCB concentration, but no detectable (LOD=0.05 µg/kg dry weight) PCBresidue in a variety of crops, including carrot. In another study, trace levels of PCBs from municipal sludge thatwas applied at a rate of about 2 metric tons/ha for two years to an old field resulted in no


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detectable PCBs in plant samples (Davis et al. 1981).Adding PCBs (Arochlor 1254) to soils to produce concentrations from 50-100 mg PCBs/kg dry soil resulted

in substantial uptake by carrot root with very little translocation to the aboveground plant parts (Iwata, et al.,1974). Computations from the data presented showed PCB concentrations in carrot root ranging from 2.7 to 15.3mg/kg with concentrations decreasing as the degree of PCB chlorination increased. Ninety-seven percent of thePCBs in the carrot root were in the peel. Although the above study showed substantial uptake by carrot root, it isunlikely that concentrations of this order of magnitude would ever occur in sludge-amended soils becauseregulations prohibit concentrations of PCBs in sludge greater than 50 mg/kg (EPA 1993a). Applying a sludgecontaining 50 mg PCBs/kg to a typical soil at a rate of 10 tons/ha would produce a concentration of 0.25 mgPCB/kg soil.

The less-chlorinated PCBs have greater potential to be taken up by the plant, but these are also much morevolatile and biodegradable, and thus are less common in sludge. The more highly chlorinated PCBs are absorbedless by plants (Fries and Marrow 1981). Lee et al. (1980) were unable to detect PCBs in carrots grown in soilcontaining 0.23 mg PCB/kg of soil derived from an application of 224 metric tons/ha of sludge containing 0.93 mgPCB/kg of sludge. Naylor and Mondy (1984) have obtained similar results with potatoes. Over 1,400 samples ofsoil and crop tissue were analyzed in a greenhouse and field study for the Madison Metropolitan Sewage District(Gan and Berthoex, 1994). No PCB translocation into either corn grain or corn stover samples occurred. It wasconcluded that little, if any, PCB will be translocated from contaminated soil to plant tops. Apparently, PCBexposure via the plant/soil pathway is minimal.

Webber et al. (1994) determined concentrations of PCBs in corn, cabbage and carrots grown on coal refuseamended with sewage sludge at rates of 785; 1,570; and 3,360 tons per ha. Concentrations of PCBs in the treatedcoal refuse ranged from 1.3 to 3.7 mg/kg and were not related to treatment. The PCB concentrations in all tissueswere less than 0.3 mg/kg; concentrations in carrot peels were greatest, followed in decreasing order by carrot tops;cabbage wrapper, inner leaves, and carrot core; corn ear leaf, stover, and corn grain. In general, the concentrationsof PCBs in the plant tissues were independent of the PCB concentration in soil. Webber et al. (1994), Witte et al.(1988), and O'Connor et al. (1991), conclude that PCBs in municipal sludges represent no significant risk to cropsor crop consumers.

Although most reports show PCB uptake by crops grown on sludge-amended soil to be negligible, Baker etal. (1980) found that PCB concentration in vegetables grown on garden soils were significantly higher than that ofthe control soil. However, concentrations of PCBs in the sludge used for that study averaged 479 mg/kg and wouldbe banned from land application by present-day federal regulations.

Chlorinated Pesticides

Some important chlorinated pesticides include aldrin, chlordane, DDD, DDE, DDT, endrin, dieldrin,heptachlor, lindane, and toxaphene. While the use of these pesticides are banned, there are many other approvedpesticides that are applied to food crops in the course of normal agricultural operations. The use of approvedpesticides is regulated by governmental


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agencies, and pesticide residues are closely monitored by food processors to prevent contamination of processedfood products. Although no longer used in the United States, many of the banned pesticides persist in theenvironment. Their presence in treated sludge or reclaimed wastewater that is applied to agricultural land used forfood crop production may be viewed by food processors as an additional uncontrollable pesticide burden, and theyhave expressed concern about their product quality being compromised when treated sludge and wastewater areused in food crop production (National Food Processors Association, 1992). Residues of aldrin and dieldrin weredetected in 3 and 4 percent, respectively, of the 209 sludges surveyed in the NSSS, at concentrations of 0.002 mg/kg and at LOD, respectively (Kuchenrither and Carr, 1991). Studies in the late 1980s reported medianconcentrations in sludges for the pesticide compounds listed above to be very much less than 1 mg/kg dry weightand, frequently, below detection limits (0.05 mg/kg) (EPA, 1990). Application rates of sludges with such medianconcentrations would result in concentrations in plant growth media of less than 0.01 mg/kg. Pot and field studies(Baxter et al., 1983; Kampe, 1989; Singh, 1983; Witte et al., 1988), some of which spanned 30 years, found thatsludge additions failed to measurably increase the level of chlorinated pesticides and hydrocarbons abovebackground soil levels. In a study involving the application of municipal sludge to coal refuse at a rate of 3360tons/ha, Webber et al. (1994) observed sludge concentrations of organochlorine pesticides ranging from less than0.015 mg/kg (heptachlor, aldrin, pp'-DDT, lindane, hexachlorobutadiene, and hexachlorobenzene) to 0.217 mg/kg(pp'-DDE). Other pesticides and their concentrations (in mg/kg) include alpha and gamma chlordane (0.08 and0.125), dieldrin (0.042), and pp'-DDD (0.091). Levels of the pesticides in corn, cabbage, and carrot tissues grownon the sludge-treated coal refuse were less than the method's detection limit of 0.1 mg/kg dry weight. Based on theinformation presented, it seems reasonable to conclude that it is highly unlikely that pesticides in sludge applied toland will harm crops or their consumers.

Disinfection Products

In United States, the treatment and discharge of municipal wastewater are governed by regulations derivedfrom federal legislative mandates in P.L. 92-500 as well as state statutes. The current regulations considerdisinfection as an important element of wastewater treatment when necessary to protect public health. Whileseveral options are available, chlorination is by far the most commonly used disinfection process for wastewatereffluents.

Rook (1976) discovered that chlorine used in disinfection reacts with naturally occurring humic substances inthe water to form trihalomathanes (THMs), the most prevalent species among them are chloroform,bromodichloromethane, dibromochlorimethane, and bromoform. Subsequent surveys of municipal water suppliesin the United States found that THMs were log-normally distributed with median concentrations less than 30 µg/1.Bellar et al. (1974) found that chloroform also formed during the chlorination of wastewater effluents. Jolley(1975), Glaze and Henderson (1975), and Glaze et al. (1978) evaluated other chlorine-containing compounds thatalso form, including chlorophenols, chlorbenzoic and chlorphenylacetic acids, and chlorinated purines andpyrimidines.

Byproducts of water and wastewater chlorination are subjects of continuous investigations


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worldwide (Johnson and Jensen, 1986; Badaway, 1992). Based on their concentrations in chlorinated wastewatereffluents and their fate and transport characteristics, it seems unlikely that they will persist in the receiving soil orbecome bioaccumulated to any great extent (Jolley, 1978; Howard, 1989). Although actual data on the persistenceof these byproducts on food crops are lacking, their presence should not limit the use of reclaimed water for cropirrigation.

Acid-Extractable Organic Compounds

Phenols, including pentachlorophenol (PCP) and 2,4-dinitrophenol (DNP), are important acid-extractableorganic compounds. Their toxicity to plants is pH-dependent. Toxicity and soil sorption are greatest in acid soils,and their degradability and mobility in soil are greatest in near neutral to alkaline conditions. Studies of PCP andDNP in high pH soils found soil degradation to be rapid. O'Connor et al. (1991) concluded that when soilsamended with sludges containing median concentrations of phenols (from NSSS, EPA 1993b) are managedaccording to sound agronomic practices of pH control, neither DNP or PCP will persist in soils long enough toimpact plants, and little plant contamination is expected.

Chlorinated Dibenzo-p-dioxins (CDDs) and Dibenzofurans (CDFs).

Like PAHs, dioxins are generally formed by combustion of organic solids, and they have been reported insludge quality surveys. In a literature review of studies of plants exposed to dioxin-contaminated soils, Kew et al.(1989) found that root uptake and translocation of tetrachlorodibenzodioxin (TCDD) was minimal, but thatsignificant contamination may occur by volatilization of TCDD from soil and absorption by foliage. Facchetti etal. (1986) concluded that volatilization would be the dominant process of transfer from soil to plant, if it were tooccur. Nevertheless, O'Connor et al. (1991) concluded that contamination of plants with either CDDs or CDFswould be unlikely due to their very low bioavailability. Even if present at high initial concentrations, dioxins insludge would be diluted at least 100-fold at agronomic sludge application rates, and the organic matter with thesludge would increase soil sorption capacity and likely reduce volatilization.

Volatile Aromatic Compounds (VOC)

Although volatile aromatic compounds (e.g., toluene, benzene, xylene) in municipal wastewater are largelylost by volatilization in the sewer or at the treatment plant, they have been detected in sludges (Jacobs et al.,1987). Benzene was detected in 93 percent of the municipal sludge samples analyzed in the 40 Cities Survey(EPA, 1982) with a mean concentration of 1.8 mg/kg; however, some fraction of these sludges were untreated, andtherefore not eligible for land application under current regulations. Benzene was detected in less than 2 percent ofthe sludges from 209 treatment plants in the NSSS in a range of concentrations from 0.01 to 0.2 mg/kg. Whensludges are applied to soils, volatile aromatics are rapidly lost due


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to volatilization. Jin and O'Connor (1990) and concluded that volatile aromatics do not persist long enough insludge-treated soils to represent a problem for agriculture under normal aerobic soil conditions. However,anaerobic conditions resulting from both bacterial depletion of oxygen due to high organic carbon content and lackor reaeration due to water-logging can promote temporary volatile aromatic retention in soil (Jin and O'Connor1990). This source of volatile organics should not pose a problem since crops, except for rice, are not grown inwaterlogged soils. Some investigators have reported contamination and bioconcentration of toxic volatile aromaticcompounds in plants (Facchetti et al., 1986). O'Connor et al. (1991) suggested that further research was necessaryto study possible plant contamination by sorption of chemical vapors from volatile aromatic compounds and othervolatile organic compounds (e.g., toxaphene, and TCDD).

Generalizations Regarding Uptake of Organics by Plants

Plant bioconcentration factors for most toxic organics are small and are often not significantly different fromzero. Most toxic organics occur in sludge at low concentrations and when the sludge is applied to soil, theirconcentrations are further diluted. Furthermore, toxic organic compounds that are not destroyed bybiodegradation, chemical oxidation, or photolysis are so strongly sorbed to the sludge-soil particulate matrix as tohave low bioavailability to plants. Many of the organic compounds are chemically or biologically degraded orvolatilized from the soil during the cropping season. Finally, because the fraction of sludge-borne toxic organicsthat does remain in soil has low bioavailability, absorption by crops is negligible. In some cases, volatile toxicorganics may contaminate plant tissue through absorption of volatilized compounds; however, managementpractices, such as incorporation of sludge with soil and application of sludge before plant sprouting, willsubstantially reduce any plant exposure to VOCs.

Available data indicate that potentially harmful toxic organic pollutants do not enter edible portions of plantsthat are irrigated with treated municipal wastewater. Irrigation of vegetables in test plots with wastewaters hasshown no accumulation of PAHs, especially benzo(a)pyrene (Il'nitskii et al. 1974). In a study of aldehydes andother organics at agricultural land treatment sites, Dodolina et al. (1976) found no uptake of acetaldehyde,crotonaldehyde, and benzaldehyde in the aboveground portions of potatoes and corn. Cyclohexanone andcyclohexanol could be found in corn plants four days after irrigation, but not later. Dichloroethane was taken up bybeets and cereals, but was metabolized and absent within about two weeks after irrigation. Although thesecompounds are found in crops and soils, they appear to be metabolized at a rate sufficient to prevent theiroccurrence in the harvested product.

Uptake of Toxic Organics by Animals

Toxic organic compounds present in plant tissues (and soil in the case of pastured animals) may beincorporated into animal tissues. However, the low levels of toxic organic compounds to be expected in theaboveground portions of plants growing at land application sites


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pose little hazard to animals feeding upon them. Under certain site-specific conditions, however, highconcentrations of particular organic compounds in the sludge may cause problems.

In considering the pathways for exposure of humans to toxic organic compounds in sludge, Chaney (1985)suggests that direct ingestion of the sludge-soil mixture by animals is the only reasonable route by which toxicorganic chemicals have been traced directly from sludge to animal products. However, the transfer of toxic organiccompounds to the human food chain via this pathway is still considered to be negligible.

FATE OF AND EXPOSURE TO TRACE ELEMENTS IN SLUDGE

The availability of inorganic chemicals or trace elements for uptake by plants (and thus entry into the humanfood chain) or transport to ground water is limited by the extent to which these elements remain free in the soilsolution. The binding of chemicals to the soil substrate is controlled by the chemical processes of complexation toorganic matter, adsorption, and precipitation. Adsorption occurs on organic matter, hydrous oxides of iron andmanganese, clays, and other soil minerals. Precipitation reactions include the formation of sparingly solubleoxides, hydroxides, carbonates, phosphates, and sulfides, etc. Mercury may leave the soil through volatilization.As a result of these processes, only small amounts of the trace elements remain free in the soil solution where theywould be available for absorption by plant roots. These processes are strongly affected by soil pH, with cationlevels decreasing and anion levels increasing in the soil solution with increasing pH (Logan and Chaney, 1983).

Chaney (1980) introduced the concept of the "soil-plant barrier" for consideration of potential toxicity to thefood chain if trace elements are applied to soils. After a trace element enters the root cells, translocation to otherplant organs (tubers, shoots, leaves, fruits, seeds), depends on the properties of the specific element and the plant.Important plant processes are membrane surfaces, organic chelators, and cells specialized for pumping materialsinto the xylem, through which it reaches the shoot. One group of metals are so insoluble or so strongly adsorbed tosoil or plant roots that they are not translocated into edible plant parts regardless of quantities present in the soil.Elements like trivalent chromium, mercury, and lead are examples. Lead is so insoluble inside the plant root andmercury is so strongly bound inside the fibrous plant roots that harmful levels of these elements are not found inedible plant parts (Berthet et al., 1984; Naylor and Mondy, 1984). Mercury can be transferred throughvolatilization from the soil surface to plant foliage, but this route is not very relevant to sludges because they arelow in mercury.

Copper and zinc belong to another group of elements that are translocated to vegetative parts of the plant.However, before they reach levels in crops that could be potentially harmful to consumers, crop growth is soseverely stunted that they are not harvestable. Phytotoxicity thus prevents excessive plant concentration ofcontaminants to levels harmful to animals, and the food chain is protected (see Chapter 4).

There are exceptions to protection by the soil-plant barrier. These exceptions have been the focus of intenseresearch in agriculture. Livestock have been injured by forage grown on soils with excessive geochemically-derived selenium (Mayland, 1994) or molybdenum (Mills and Davis, 1987) for centuries. Cadmium is absorbed bycrops and can reach levels that are dangerous


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to humans if a high percentage of the consumer's diet is derived from crops grown on cadmium-contaminated soilover an extended time period. Human disease from soil cadmium occurred in Japan where mining wastes pollutedpaddy rice fields, and farm families consumed the rice grown on these paddies for 40 or more years (Kobayashi,1978; Nomiyama, 1986). It should be noted that the diets of the Japanese families were low in calcium and zinc.Calcium, iron, and zinc play major roles in interfering with cadmium absorption in the human intestine (Fox,1988), and when sufficiently present in the human diet, high cadmium foods will not always produce healtheffects.

Selenium toxicity to humans has been documented in China (Combs and Combs, 1986); however, the sourceof the selenium was not municipal sewage sludge. Municipal sewage sludges are not high in selenium. Similarlyfor livestock, soil molybdenum is a potentially toxic element, but no cases have been reported of molybdenumtoxicity to animals from consumption of forage grown on sludge-amended soils. In pot studies, where clover wasgrown on alkaline soils containing up to 16 kg of molybdenum per ha, concentrations in the plant tissue reachedlevels that could be harmful to animals if the clover were to make up a substantial portion of the diet for anextended period of time (Davis, 1981). Burau et al. (1987) collected five years of field data on the impact oftreated municipal wastewater on trace element concentrations in soil and vegetables. They concluded that therewas no significant difference in concentration between food crops irrigated with treated domestic wastewater andwellwater. They did observe, however, that commercial fertilizer application did result in increased plant tissuelevels of some metals, such as cadmium, zinc, and manganese. Levels in plants, however, were well below thoseconsidered harmful.

The uptake of trace elements by plants has been reviewed by Logan and Chaney (1983). Important factorsaffecting uptake rate include: trace element properties, soil properties, the immediate environment (especially pH)of the roots, plant crop species, and plant crop cultivar (variety or strain). As an example of species effects, leafyvegetables, especially Swiss chard, are much better cadmium accumulators than most other plants. Cultivars ofmaize (corn) and wheat have been shown to vary in their rates of cadmium accumulation.

Uptake of Trace Elements by Animals

As with toxic organics, animals can be exposed to trace elements through sludge residuals adhering to plants,sludge on the soil surface or mixed into the soil, or trace elements absorbed and translocated by plants. All threeroutes can operate on grazing land, but only the third is relevant when animals are given feed grown on sludge-amended soils.

At Werribee Farm in Melbourne, Australia, cattle are grazed on wastewater-irrigated pastures and showhigher organ levels of cadmium and chromium than farm cattle grazed on nonirrigated pastures, although elevatedlevels were within the range common to cattle in general (Croxford, 1978). Organ levels of lead, however, did notincrease, in spite of lead increases in both soil and pasture plants. Dowdy, et al. (1983) fed silage grown onsludge-amended soils to goats and sheep for a period of three years. The silage contained up to 5.3 mg cadmium/kg, a concentration 10 or more times greater than normal silage. Cadmium and zinc were elevated in the kidneyand liver but not in the muscle tissue. Concentrations of copper, nickel, chromium,


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lead and zinc in organs of animals fed silage from sludge-amended soils did not differ from animals fed a similardiet of forage from lands not receiving sludge. The concentrations of cadmium in the milk of goats that were fedthe treated silage did not differ from controls (Dowdy et al., 1983). Telford et al. (1984) also reported that theconcentration of cadmium in milk from goats fed silage from sludge-amended soils over a period of 135 days didnot differ from the controls. Silage from the sludge-amended soils contained up to 3.8 mg cadmium/kg; controlsilage contained 0.14 mg cadmium/kg. Concentrations of cadmium in the livers of adult goats fed silage from thesludge-amended soils were significantly greater than the controls.

Studies of the accumulation of trace elements in cattle grazed on sludge-amended pastures have revealedelevated levels in liver and kidney, but not in muscle tissue (Bertrand et al. 1981a, Baxter et al. 1983). Sheepgrazing on sludge-amended pasture had no statistically significant increases in tissue levels of cadmium (Hogue etal. 1984). Bertrand et al. (1981b) observed no increases in metal concentration of cattle fed sorghum grown onsludge-amended soil nor did increases occur in tissues of mice or guinea pigs fed lettuce and Swiss chard grown onsludge-amended soil (Chaney et al., 1978a,b). Other studies, however, have shown significant increases ofcadmium in kidney and liver, but not in muscle tissue of animals fed sludge-fertilized crops (Hansen and Hinesly,1979; Lisk et al., 1982; Hinesly et al., 1984; Bray et al., 1985; Hogue et al., 1984). Trace element levels anddisease conditions of cattle grazing on land reclaimed using Chicago sludge have been observed by Fitzgerald etal. (1985) for up to eight years; they concluded that little risk to man or animals is associated with land applicationof anaerobically digested wastewater sludge. All cattle remained healthy and no pathological changes could beattributed to sludge.

Based on these studies, it appears that trace elements either do not accumulate or accumulate in very smallquantities in animal muscle tissue. However, cadmium and other metals do accumulate in the liver and kidneys ofanimals.

The current state of knowledge allows the following generalizations to be made: Elements potentiallyharmful to consumers which may accumulate in crops include cadmium (humans, animals), molybdenum(animals), and selenium (animals). Cadmium accumulates in the liver and kidney of animals fed crops grown onsludge-amended soils. Although levels of cadmium in foods grown on sludge-amended soil are elevated, there areno documented cases of human or animal poisoning from this source.

NONSPECIFIC HEALTH EFFECTS OF SLUDGE AND WASTEWATER

Although a large number of organic and inorganic constituents of sewage have been identified in the PriorityPollutants list and additions as discussed above, some of the residual fraction that is unidentified may havenonspecific human health effects. Investigations of non-specific or general health effects normally consist ofresearch on non-human organisms as explained below.

Nonspecific toxicological testing of whole reclaimed water using the Ames Salmonella Microsome MutagenAssay and the Mammalian Cell Transformation Assay have been used to indicate the potential of mutagenic,cytotoxic, and carcinogenic effects on bacterial and mammalian cells (Nellor et al., 1984). Clevinger et al. (1983)performed bioassays on five sludges using


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the Ames test and found that none had significant mutagenic effects. In another large study where concentratedreclaimed wastewater was given to several species of test animals for two years, no acute or chronic health ordevelopmental effects were found (Lauer, 1993). The latter study is of particular interest because of itsthoroughness. The National Research Council (1982) concluded that the ''ultimate" evaluation of health effects ofreclaimed wastewater used for drinking water purposes must come from studies on whole animals. Furthermore,because of the difficulty of reliable interpretation of results of bioassay studies using single compounds isolatedfrom wastewater, test animals should be exposed to concentrates of the whole reclaimed water.

Accordingly, in a two-year animal effects testing study of reclaimed wastewater for potable reuse, the DenverWater Department compared reclaimed wastewater with Denver municipal drinking water in tests administered toanimals as drinking water (Lauer et al., 1990). Matched groups of Fischer 344 rats and B6C3F1 mice were used totest for acute and chronic (including carcinogenic) health effects over the 104-week study, and Sprague-Dawleyrats were used for a two-generation reproductive toxicity study. The results of chronic toxicity/ carcinogenicstudies of both rats and mice showed no significant differences in clinical pathology (hematology, clinicalchemistry, and urinalysis) and gross pathology. Similarly, no significant difference were found in the formation ofneoplasms between reclaimed water-fed mice and rats and controls fed both treated drinking water and distilledwater. Finally, there were no demonstrated effects from the ingestion of reclaimed water on reproductiveperformance, fetal development, offspring survival or growth during the two-year reproductive study (Lauer,1993).

A number of studies have been conducted on the effects of feeding sewage sludges to animals either directlyor where animals have ingested sewage sludge that was sprayed on forage. Where cattle were fed up to 12 percentof their diet from sludge for 94 days, or 6 percent of their diet for 141 days, no adverse health effects were noted(Keinholz et al., 1979; Bertrand et al., 1981a). No adverse effects were noted when baby pigs were raised on a dietconsisting of 5 percent sludge for a period of one month (Firth and Johnson, 1955). Rats and Japanese quail feddiets with 30 percent sludge 2 weeks showed no adverse health effects (Cheeke and Meyer, 1973). Baby chicksconsuming a diet consisting of 10 percent sludge for about one month showed no adverse health effects (Firth andJohnson, 1955); where 20 percent of the diet of birds came from sludge, however, body weight gain and livervitamin A were found to be reduced (Keinholz, 1980). In a four-year study, where 7 percent of the dry matter ofthe diet of breeding ewes consisted of sludge sterilized by gamma irradiation, Smith et al. (1985) reported noaccumulation of hazardous levels of toxic elements and little, if any, evidence of toxicity. Johnson et al. (1981) fedHereford steers a diet that included 11.5 percent sewage sludge and observed retention of dietary cadmium,mercury and lead to be 0.09 percent, 0.06 percent and 0.3 percent, respectively. Concentrations of these elementsin the liver and kidneys of steers were found to increase from 5- to 20-fold following sludge ingestion. Theauthors' data showed that less than 0.3 percent of the sludge-fed cadmium, mercury, and lead were retained by thecattle. These data indicated that cattle are a moderately effective screen against entry of toxic elements fromsludge into the human food chain. Damron et al. (1982) substituted 7 percent sludge in the diet of white Leghornhens for a period of 84 days and observed no effect on bird performance; egg production was unaffected and noincrease in cadmium was found in the eggs.


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Keinholz (1980) cited a study of PCBs in cabbage grown on sludge-amended soil that was reportedly linkedto degenerative changes in liver and thyroid of sheep (Haschek et al., 1979, cited by Keinholz, 1980). However,the study involved cabbage grown in sludge that contained 17 mg/kg PCBs, an unusually high concentration andabout twice the maximum observed in the NSSS. Adding this sludge to soil at an agronomic rate would result in aPCB concentration in soil of less than 0.1 mg/kg in the surface 20 centimeters. Therefore, it is unlikely that sludgecontaining even this high a concentration of PCBs would be harmful if applied to agricultural land according topresent-day regulations and guidelines.

Hansen et al. (1976) studied young swine fed for 56 days on corn grown on sludge-fertilized land.Electroencephalograms, electrocardiograms, clinical chemistry, and histopathology were all normal. However,they did observe elevated levels of hepatic microsomal mixed function oxidase (MFO) activity. This increasedMFO activity may have been caused by toxic organics and inorganic trace elements in the sludge, and the authorsconcluded that further study should be performed before such grain can be recommended as the major dietarycomponent for animals over long periods.

An epidemiologic study on human exposure to pathogens in sludge compared health effects in 164 peopleliving on 47 farms which received 2 to 10 tons of sludge per ha per year for three years to 130 people from 45farms who formed a control group. Both study groups were from geologically matched areas of rural Ohio. Studyparticipants answered monthly surveys and had annual tuberculin testing and serological tests of quarterly bloodsamples. In addition, monthly surveys included questions about farm animals' health. It was found that there wereno significant differences in the health of those living on farms where sludge was applied compared to the controlgroup with respect to respiratory or digestive illness or other reported physiological symptoms. Similarly, nodifferences were reported between domestic animals from sludge-amended versus control farms (Brown et al.,1985).

SUMMARY

A review of the literature for toxic organics and for inorganic trace elements in treated municipal wastewatereffluents or treated sewage sludge indicates that most of these chemicals are either not transferred from soil toplant tissues or that translocation to edible tissues does not reach levels harmful to consumers under normalagricultural conditions.

With regards to human health concerns about the use of treated sludge on crops, the inorganic chemicalconsidered to be of greatest concern is cadmium. This conclusion is consistent with the policy approach taken tominimize health risks due to chemicals from land application of sewage sludge.

Research on the bioavailability of toxic organic compounds to plants indicates that the risk to humansconsuming food crops grown on soils amended with sludge is negligible. Toxic organic compounds are typicallypresent at such low concentrations and/or are largely not bioavailable to plants, that they would accumulate onlyat very low concentrations, if at all, in edible portions of plants.

Few adverse health effects have been found in studies where treated sludge and treated effluent were feddirectly to animals. No adverse human acute or chronic toxicity effects have


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been reported resulting from ingestion of food plants grown in soils amended by sludges or crops irrigated byreclaimed water.

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Alexander, M. 1994. Biodegradation and Bioremediation. San Diego, Calif.: Academic Press, 302 pp.Atlas, R. M. 1981. Microbial degradation of petroleum hydrocarbons: An environmental perspective. Microbiol. Rev. 45:180–209.Aranda, J. M., G. A. O'Connor, and G. A. Eiserman. 1989. Effects of sewage sludge on di(2-ethylhexyl)phthalate uptake by plants. J. Environ.

Qual. 18:45–50.Badaway, M. I. 1992. Trihalomethane in drinking water supplies and reused water. Bull. Environ. Contam. Toxicol. 48:157–162.Baker, E. L., Jr., P. J. Landrigan, C. J. Gluek, M. M. Zack, Jr., J. A. Lidde, V. W. Burse, W. J. Housworth, and L. L. Needham. 1980.

Metabolic consequences of exposure to polychlorinated biphenyls (PCB) in sewage sludge. Am. J. Epidem. 112:553–560.Baxter, J. C., D. E. Johnson, and E. W. Kienholz. 1983. Heavy metals and persistent organics content in cattle exposed to sewage sludge. J.

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steers grazing on Pensacola Bahiagrass pastures treated with liquid digested sludge. J. Animal Sci. 53:146–163.———. 1981b. Animal performance, carcass quality, and tissue residues with beef steers fed forage sorghum silages grown on soil treated

with liquid digested sludge. Proc. Soil Crop Sci. Soc. Florida 40:111–114.Bossert, I. D., and R. Bartha. 1986. Structure-biodegradability relationships of polycyclic aromatic hydrocarbons in soil. Bull. Environ.

Contam. Toxicol. 37:490–495.Bray, B. J., R. H. Dowdy, R. D. Goodrich, and D. E. Pamp. 1985. Trace metal accumulations in tissues of goats fed silage produced on sewage

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———. 1985. Potential effects of sludge-borne heavy metals and toxic organics on soils, plants, and animals, and related regulatoryguidelines. Pp. 1–56 in Final Report of the Workshop on the International Transportation, Utilization or Disposal of Sewage SludgeIncluding Recommendations. PNSP/85-01. Washington, D.C.: Pan American Health Organization.

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Combs, G. F., Jr., and Combs, S. B. 1986. The Role of Selenium in Nutrition. New york: Academic Press, 532 p.Cork, D. J., and J. P. Krueger. 1991. Microbial transformations of herbicides and pesticides. Advan. Applied Microbiol. 36:1–66.Croxford, A. H. 1978. Melbourne, Australia, Wastewater System: Case Study. 1978 Winter Meeting, Chicago, Illinois. Amer. Soc. Agric.

Eng. Paper No. 78-2576. St. Joseph, Michigan.Damron, B. L., H. R. Wilson, M. F. Hall, W. L. Johnson, O. Osuna, R. L. Suber, and G. T. Edds. 1982. Effects of feeding dried municipal

sludge to broiler type chicks and laying hens. Polut. Sci. 61:1073–1081.Davis, R. D. 1981. Uptake of molybdenum and copper by forage crops growing on sludge-treated soils and its implication for the health of

grazing animals. Pp. 194–197 in Proc. Intl. Conf. on Heavy Metals in the Environment, CEP Consultants, Edinburgh, Scotland.Davis, T. S., J. L. Pyle, J. H. Skillings, and N. D. Danielson. 1981. Uptake of polychlorobiphenyls present in trace amounts from dried

municipal sewage sludge through an old field ecosystem. Bull. Environ. Contam. Toxicol. 27:689–694.Dean, R. B., and M. J. Seuss. 1985. The risk to health of chemicals in sewage sludge applied to land. Waste Manage. Res. 3:251–278.Dodolina, V. T., L. Y. Kutepov, and B. F. Zhirnov. 1976. Permissible quantities of organic substances in wastewaters used for irrigation.

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sewage sludge. J. Anim. Sci. 51:108–114.Johnson, J. D. and J. N. Jensen. 1986. THM and TOX formation: routes, rates, and precusors. J. Amer. Water Works Assoc. 78:156–161.Jolley, R. L. 1975. Chlorine-containing Organic Constituents in Chlorinated Effluents. J. WPCF 47:601–618.———., ed. 1978. Water Chlorination: Environmental Impact and Health Effects. Ann Arbor, Mich.: Ann Arbor Publishers.Kampe, W. 1989. Organic substances in soils and plants after intensive application of sewage sludge. Pp. 180–185 in Sewage Sludge

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Kew, G. A., J. L. Schaum, P. White, and T. T. Evans. 1989. Review of plant uptake of 2,3,7,8-TCDD from soil and potential influences onbioavailability. Chemosphere 18:1313–1318.


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Kobayashi, J. 1978. Pollution by cadmium and the itai-itai disease in Japan. pp. 199–260 in Toxicity of Heavy Metals in the Environment. F.W. Oehme, ed. New York: Marcel Dekker.

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Lauer, W. C., F. J. Johns, G. W. Wolfe, B. A. Meyers, L. W. Condie, and J. F. Borzelleca. 1990. Comprehensive health effects testing programfor Denver's potable water reuse demonstration project. J. Toxicol. & Environ. Health 30:305–321.

Lauer, W. C. 1993. Denver's direct potable water reuse demonstration project. Final report. Denver, Colo.: Denver Water Department.Lee, C. Y., W. F. Shipe, L. W. Naylor, C. A. Bache, P. C. Wszolek, W. H. Gutenmann, and D. J. Lisk. 1980. The effect of a domestic sewage

sludge amendment to soil on heavy metals, vitamins, and flavor in vegetables. Nutr. Rep. Int. 21:733–738.Lin, D. 1980. Fate of petroleum hydrocarbons in sewage sludge after land disposal. Bull. Environ. Contam. Toxicol. 25:616–622.Lisk, D. J., R. D. Boyd, J. N. Telford, J. G. Babish, G. S. Stoewsand, C. A. Bache, and W. H. Gutenmann. 1982. Toxicological studies with

swine fed corn grown on municipal sewage sludge-amended soil. J. Animal Sci. 55:613–619.Logan, T. J., and R. L. Chaney. 1983. Metals. Pp. 235–323 in Utilization of Municipal Wastewater and Sludge on Land. A. L. Page, T. L.

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7

Regulations Governing Agricultural Use of MunicipalWastewater and Sludge

Government regulations at both the federal and state levels develop within a complex set of circumstances. Tofully understand them, regulations must be examined in terms of the regulatory approach taken, the underlyingscientific principles that are applied, the objectives of the regulation, and the effectiveness of implementation. Thefollowing section begins with a discussion of the regulatory background for agricultural use of municipalwastewater and sludge. Current federal standards for control of pathogens and toxic chemicals in sludge use arethen described and evaluated. Finally, state regulations and United States Environmental Protection Agency (EPA)guidelines for agricultural irrigation with treated effluents are discussed.

The implementation of wastewater and sludge reuse programs also involves other regulatory components,including program management, surveillance, and enforcement. Economic considerations, liability issues, andpublic concerns will likewise play a role. These implementation issues are considered in Chapter 8.

REGULATORY BACKGROUND

Agricultural Irrigation with Wastewater

Irrigation of crops with treated effluent and farmland application of sewage sludge have been conductedwithout federal regulations for decades in the United States. Early regulations by states addressed infectiousdisease transmission and the reduction of odor. Wastewater irrigation continues to be regulated at the state level,and those states (such as Arizona, California, Florida, Hawaii, and Texas) that have active water reuse programshave developed comprehensive, numerical water quality criteria for different water uses, including crop irrigation.Pathogen reduction continues to be the major concern, and microbiological limits for treated effluents are basedlargely on practical experience within the public health community, and on the expected performance ofwastewater treatment processes. There have been no reports of infectious disease associated with agricultural reuseprojects, and existing criteria are considered to be adequate (see Chapter 5). Most states distinguish betweenproduce (or crops that

REGULATIONS GOVERNING AGRICULTURAL USE OF MUNICIPAL WASTEWATER AND SLUDGE 120

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can be eaten raw) from crops that are commercially processed or cooked prior to consumption, and require morestringent water quality levels for produce crops.

Nevertheless, states differ in the manner in which wastewater irrigation can be implemented. For example,California, with the longest history of regulating reclaimed wastewater for agricultural use, permits high-qualityeffluents to be used on produce crops. Florida normally restricts the agricultural use of reclaimed water to thosefood crops that are skinned, cooked, or thermally processed before consumption (EPA, 1992).

Chemical pollutants in treated municipal wastewater have not been targeted by state regulations for reclaimedwater. This is because the concentrations of these pollutants in effluents that receive a minimum of secondarytreatment are comparable to those in conventional sources of irrigation water, and the reclaimed water generallymeets current irrigation water quality criteria (e.g., Wescot and Ayers, 1985) for chemicals that are potentiallyharmful to crop production or to ground water contamination (see Chapters 2 and 4 for further discussion). Sourcecontrol of industrial inputs, conventional secondary treatment, and advanced treatment are relied upon to reduceeffluent concentrations of chemical pollutants to levels that do not impact the particular end use.

Agricultural Use of Sewage Sludge

Sewage sludges are recognized as potentially harmful because of the chemical pollutants and the disease-causing agents they may contain. Prior to the early 1970s, there was no direct legislative authority for any federalagency to regulate sludge disposal. In 1972, Congress directed EPA to regulate the disposal of sludge enteringnavigable waters through Section 405(a) of the Federal Water Pollution Control Act. The Resource Conservationand Recovery Act (RCRA) of 1976 (P.L. 95–512) exempts sewage sludge from hazardous waste managementregulation in cases where industrial discharges to the publicly owned treatment plant (POTW) are alreadyregulated under EPA-approved pretreatment programs. In 1977, Congress amended section 405 of the FederalWater Pollution Control Act to add a new section, 405(d), that required EPA to develop regulations containingguidelines for the use and disposal of sewage sludge on land as well as in water. These guidelines were to (1)identify alternatives for sludge use and disposal; (2) specify what factors must be accounted for in determining themethods and practices applicable to each of the identified uses; and (3) identify concentrations of pollutants thatwould interfere with each use. Federal criteria (40 CFR Part 257) identifying "acceptable solid waste disposalpractices—including landfill and land application—were issued in 1979 under the joint authority of RCRA(Subtitle D) and the Clean Water Act (Section 405). These criteria specified limits on cadmium in sludge and soilpH levels, limited the soil incorporation of sludges with greater than 10 mg/PCB/kg, and contained criteria forpathogen reduction. However, these criteria for sludge use and disposal were not widely used.

In 1987, Congress once again amended Section 405 to establish a timetable for developing technicalstandards for sewage sludge use and disposal (Water Quality Act of 1987, P.L. 100-4). Congress directed EPA toidentify toxic pollutants that may be present in sewage sludge in concentrations that may affect public health andthe environment, and to specify acceptable management practices and numerical limits for sludge that containthese pollutants.


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These regulations were to be ''adequate to protect the human health and the environment from any reasonablyanticipated adverse effect of each pollutant." (Section 405(d)(2)(D)). Section 405 was also amended to specifythat technical standards for sludge use and disposal be included in any permit issued to a POTW or other treatmentworks. The final "Standards for the Use and Disposal of Sewage Sludge" were promulgated in 1993 by the EPA(40 CFR 503, EPA, 1993a) and are referred to as the "Part 503 Sludge Rule" in this report.

FEDERAL STANDARDS FOR THE CONTROL OF PATHOGENS IN SEWAGE SLUDGE

Standards and management practices for the reduction of pathogens to acceptable levels prior to human oranimal contact and vector attraction reduction are major aspects of the Part 503 Sludge Rule. Based upon pathogenreduction criteria, the Rule divides sludge into two categories, Class A (safe for direct contact) and Class B (landand crop use restriction supply). Class A sewage sludge can be used in an unrestricted manner. Class A pathogenrequirements (shown in Table 7.1) must be met by one of six alternatives and use of either the fecal coliform orsalmonella tests as described below.

In Part 503, all Class A sludges must meet either a fecal coliform limit of less than 1,000 fecal coliform/g dryweight of solids or a measure of less than 3 salmonella/4 g dry weight of solids (EPA, 1993a). As discussed inChapter 5, the threshold of 1,000 fecal coliform/g dry weight appears reasonable given that all evidence points toequal or greater resistance of fecal coliforms in comparison to other common bacterial pathogens such assalmonella. When the numbers of fecal coliforms in raw sludge are in the range of 10,000,000/g, then thereduction to 1,000/g would indicate a similar rate of reduction in bacterial pathogen numbers. For example, theconcentration of salmonella in raw sludge is estimated to be 2,000/g of solids; thus, a five log10 reduction wouldreduce the salmonella level to approximately 2/100 g of solids. In a comparison of the relationship between fecalcoliform and salmonella numbers, Yanko (1988) described this same relationship.

Because of the small sample size and interference by large numbers of nonsalmonella bacteria, the methodprescribed for salmonella in Part 503 is apt to underestimate the number present in any given sludge sample (alsosee Yanko et al., 1995). The chances of finding 3 salmonella in 4 g of sludge is much less than those of finding1,000 fecal coliforms in 1 g. This may be of some concern when the salmonella determination is used in lieu of thefecal coliform assay. As stated in the Rule, to be classified as Class A, all sludges must meet either the fecalcoliform or the salmonella requirement. Because standard salmonella determination methods as now practiced arenot precise, there may be a temptation to use the salmonella test in lieu of the coliform test, regardless of theregrowth potential in the sludge.

In certain Class A processed sludges, fecal coliform regrowth may occur, in which case the sludge might notmeet the fecal coliform requirement, but the sanitary significance of the numbers would be unclear. In this instancethe Part 503 Sludge Rule allows for the direct determination of salmonella, and if their concentration is less than 3salmonella/4 g dry weight of sludge, the Class A classification would hold. Until such time as more accuratesalmonella detection methods are developed, it would be expedient to use the salmonella test only after coliform


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TABLE 7.1 Summary of Part 503 Sludge Rule Pathogen Limits For Class A Sludge

All Class A sludges must meet: fecal coliform density of < 1,000 MPNa/gram total solids.b

or

Salmonella sp. density of < 3 MPN/4 grams total solids.

Plus one of 6 alternatives:

#1 Time and temperature requirements specified, depending on solids content of sludge.

#2 Alkaline and temperature treatment requirements: pH > 12 for at least 72 hours.Temperature > 52¹C for at least 12 hours, then air dry sludge to < 50% total solids.

#3 Level of enteric virus and helminth ova prior to pathogen treatment are < 1 PFUc/4grams total solids for virus and < 1 viable ova/4 grams total solids for helminth ova.

or

If levels of enteric virus and/or helminth ova prior to pathogen treatment are < 1 PFU orif viable ova are present, then test after treatment. Document process operatingparameters to achieve < 1 PFU/4 grams total solids for virus and < 1 viable ova/4 gramstotal solids for helminth ova.

#4 Levels of enteric virus and helminth ova after treatment and when ready to distribute are <1 PFU/4 grams total solids for virus and < 1 viable ova/4 grams total solids for helminthova.

#5 Use of Process to Further Reduce Pathogens (PFRP). See requirements forcomposting, heat drying, heat treatment, thermophilic aerobic digestion, beta rayirradiation, gamma ray irradiation, and pasteurization.

#6 Treat equivalent to PFRP requirements. Determined by the permitting authority.

a MPN: Most Probable Numberb all weights are dry weightsc PFU: Plaque Forming UnitsSOURCE: EPA, 1993b

regrowth or regrowth potential has been determined, and not as an alternative to the fecal coliform methodfor determining pathogen levels in all sludges.

In addition to the fecal coliform or salmonella test, there are six alternative requirements for achieving aClass A sludge status (Table 7.1). These can be summarized as: (1) use of specified application of time andtemperature; (2) use of heat and elevated pH; (3) and (4) the demonstration of the absence of viable helminth ovaand enteric viruses either before or after some form of treatment; and, (5) and (6) an accepted process to furtherreduce pathogens (PFRP) or equivalent. The Part 503 Sludge Rule states that all the alternatives are of equal valuein that they will meet, as a minimum, the pathogen standard set forth in alternatives (3) and (4).


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At the present state of our knowledge, Class A microbial standards or process standards for sludge appear tobe adequate for public health protection. However, when relying on the direct measurement of pathogens, oneshould be aware of the accuracy and precision of the methods that are presently available. The standard may bequite adequate but the method used to determine if the standard has been met can be questionable (Cooper andRiggs, 1994).

Part 503 describes "Class B" as sludge having lesser sanitary quality than Class A at the time of application.This class of sludge is applied to land under a variety of restrictions. There are three alternative requirements thatmust be met to qualify a sludge as Class B. The first alternative requires a domestic sludge to contain a geometricaverage fecal coliform level of less than 2,000,000 bacteria most probable number (MPN)/g dry weight based onseven samples. Most wastewater and sludge treatment practices can attain this fecal coliform level. A secondalternative for meeting Class B requirements is to use designated sludge treatment processes to significantlyreduce pathogens (PSRP). Processes that meet PSRP criteria will, as a minimum, meet the coliform requirementof 2,000,000/g.

In addition to the above quality or process requirements, land use restrictions are also required for theapplication of Class B sludge. These restrictions are summarized in Table 7.2, and their rational is based on thetime required to significantly reduce the number of helminth ova. Helminth ova are among the mostenvironmentally resistant of the infectious agents, and the time required for their reduction would be more thansufficient for the reduction of bacterial and viral pathogens. The Part 503 Sludge Rule requires a 20-month timeperiod to elapse prior to harvesting root crops and a 14-month time period before harvest of other crops that touchthe ground. These criteria are based on data developed by the EPA (EPA, 1993b) that indicate a "relatively highrate of die-off of helminth ova on the soil surface" within these time periods. Lawn turf is land with a highpotential for human contact, and Feachem et al. (1983) consider a year to be a sufficient waiting period to provideadequate protection to the public from ascaris infection in this context. The 30-day restriction for nonroot oraboveground crops, feed, and fodder was considered to be adequate for the protection of public and animal health.

The analysis for the Part 503 Sludge Rule predicts greater risks to those exposed to runoff water (e.g., fromswimming) than for other pathways. Because of this concern, Part 503 urges that drainage be carefully managed.The model also predicted a greater risk to onsite workers during the initial time period of application. The greatestonsite risk calculated was 0.02 infections per 100,000 (EPA, 1993b). It should be kept in mind that the number ofindividuals exposed onsite is relatively small and thus the occurrence of infection would be limited.

The beef tapeworm, Taenia sarginata, and the pork tapeworm, T. solium , are the primary human pathogensof concern in the application of Class B sludge to fodder or grazing land. According to Feachem et al., (1983) andthe EPA model, 30 days should be a sufficient period of time for destruction of these ova; however, a more recentinvestigation in Denmark (Ilsole et al., 1991) indicated that a small proportion of the ova remained viable for 5 to 6months and were nonviable by the end of 8 to 10 months of soil exposure.

The pathogen criteria for the application of Class B sludge to land is based on information from the availableliterature and, with the exception of the waiting time criteria for fields to be used for fodder and grazing, appear toconform to that literature. Although concern is based only on a single report (Ilsole et al., 1991), it does create areservation that should be


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TABLE 7.2 Class B Sludge Application-Land Use Restrictions

Food crops that touch sludge or soil Harvest after 14 mos. of sludge application

Root crops Harvest after 20 mos. if 4 mos. elapse prior to planting

Other food, feed or fodder Harvest after 30 days of sludge application

Grazing No grazing prior to 30 days after sludge application

Lawn turf Harvest after one year of sludge application

Public access to land - high access potential one year waiting period prior to access

Public access to land - low access potential 30 day waiting period prior to access

addressed. In this country, we depend on consumer cooking of meat to destroy any helminthcysts, includingtrichina worms in pork. Managing the disposal of human waste to grazing land and meat inspections provideadditional controls. Generally, the fewer viableeggs of Taenia species allowed on grazing land, the better;however, the actual risk of a too short waiting period may not be measurable.

As stated previously, the reliability of any sludge treatment process in reducing pathogens to acceptablelevels is paramount for public health protection. There are many variables, such as pH, moisture, sunlight,temperature, and indigenous microflora, that are involved in the decay of pathogens in the soil environment. Class Bapplications rely on these natural processes for public health protection. Because of the number of uncontrollablevariables, one might assume less reliability in pathogen reduction than in the case of most Class A sludgeapplications. In this regard the use of Class B solids on fields used to grow for crops for human consumption,particularly those eaten raw, may present a greater risk than does the use of Class A materials. The absolute degreeand impact of this increased risk on public health cannot be determined but, at the present state of our knowledgeand experience, the difference in infectious disease risk appears to be imperceptible.

A second public health aspect of sewage sludge management is the potential for vector attraction, althoughthis aspect of the Part 503 Sludge Rule has not been evaluated in this study. Vectors are animals involved in thetransmission of infectious diseases to humans. In the case of sludge disposal, there is particular concern withinsect vectors that might be attracted to the disposal site as a result of management practices. The Part 503 SludgeRule recognizes this potential and has made provisions for vector attraction and nuisance reduction.

APPROACHES TO TOXIC CHEMICAL REGULATION IN SLUDGE AND WASTEWATERLAND APPLICATION

Philosophically, pollutant inputs to soils through land application of wastewater and sewage sludge may beregulated through two approaches (Chang et al. 1993). One approach is to prevent toxic chemical pollutants fromaccumulating above natural background levels in the


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soils. Another approach is to allow pollutants to accumulate so long as the soil capacity for assimilating,attenuating, and detoxifying the pollutants is adequate to minimize the risk to humans, agricultural crops, and theenvironment.

The part 503 Sludge Rule is based on the second approach, whereas regulations in several European nations,such as Holland and Norway, are based upon the first. McGrath et al. (1994) reviewed regulations controllingpollutant inputs via land application of municipal sludges in the United States and in Western Europe andcompared the benefits and disadvantages of each approach. While the scientific principles of these two approachesare both valid, the numerical limits on toxic chemicals derived from each approach may vary by orders ofmagnitude.

Preventing Toxic Chemical Pollutant Accumulation in Soils

The underlying objective of this approach is to preserve a soil's current condition and to avoid anaccumulation of pollutants from long-term applications of sludge and wastewater. This approach aims to preventan increase in the concentration of pollutants based on the assumption that any increase in pollutants wouldcompromise the soil's ability to support a productive microbial and botanical population and limit its potential use. Aland application regulation based on this approach strives to prevent pollutant accumulation in the soil fromexceeding levels that exist before sludge or wastewater effluent is applied.

To meet this objective, pollutant input from applications of wastewater or sludge and other sources must bebalanced by pollutant output via surface runoff, leaching, atmospheric loss, and plant uptake followed by removal.In soils, pollutant output is typically very low. Consequently, the pollutant loading from all sources including landapplication of wastewater and sewage sludge must also be very low in order to maintain the balance and preventany net accumulation. Regulations and guidelines that employ this principle must set very stringent toxic chemicalpollutant loading limits for soils that can only be met by preventing all toxic chemical pollutants from enteringwastewater collection and treatment systems, or by requiring the use of advanced levels of treatment to physicallystrip pollutants out of the effluent or sludge prior to land application. Otherwise, the sludges or effluents have to beapplied at very low rates to prevent no net change in the pollutant concentration in the soil.

One advantage of this approach is that detailed knowledge about the fate and transport of pollutants, exposureanalysis, and dose-response relationships is not necessary. The numerical limits for pollutants may be calculatedby simple mass balances (pollutants in sludge and/or wastewater=pollutants transported out of soil system viasurface runoff, leaching, atmospheric loss and removal by harvested plants) and this relationship can be applied toany location. However, the disadvantages are twofold: (1) meeting the numerical limits can be very costly, and (2)the allowable application rates are too low to provide any nutrient value.

Allowing Pollutant Accumulation in the Soil

The premise of this approach is that advantage can be taken of the beneficial qualities


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(moisture, organic matter and nutrients) of sludges and wastewater and of the capacity of soil to attenuate toxicchemical pollutants present in the sludges or wastewater. Soil is a dynamic medium consisting of mineralfragments, organic matter, biota, water, and air. Pollutants introduced into soil are subject to physical, chemicaland biological transformations. Consequently, pollutants introduced to soil in low amounts may not have animmediate deleterious effect. Over time, such pollutants will accumulate and when a specific concentration isreached, harmful effects can occur. This knowledge can be used to properly manage cropland application oftreated effluents and treated sludge so that the accumulation of chemical pollutants in the soil does not reach levelsthat harm exposed individuals or the environment. Under this scenario, agronomic benefits of wastewater andsewage sludge may be realized without harming soil quality, public health, and the environment.

This approach entails developing maximum permissible pollutant loading limits and/or maximum permissiblepollutant concentration for the soil. It necessitates a more complete understanding of pollutant chemistry, healthhazards, pathways to exposure, and sophisticated modeling techniques.

DEVELOPMENT OF U.S. CHEMICAL POLLUTANT STANDARDS FOR AGRICULTURALUSE OF SEWAGE SLUDGE

The part 503 Sludge Rule defines the domain within which sewage sludges may be safely disposed orbeneficially used (EPA, 1993a). The sludge management options addressed by this regulation include agriculturalland application, nonagricultural land application, sludge-only landfills, surface disposal, and incineration. Thisreport is concerned with agricultural land application of sludge. For this use, the regulation sets numerical limits oncumulative loadings for certain pollutants, defines the sludge- processing requirements necessary to controlpathogens and parasites, and outlines an implementation plan. Requirements for nonagricultural land application,including home or horticultural use, are derived from the requirements for agricultural land application.

EPA used a risk assessment approach to develop the standards for chemical pollutant limits in the Part 503Sludge Rule. In performing the assessment, EPA followed a framework presented by the National ResearchCouncil (NRC, 1983). EPA's approach is premised on the condition that chemical pollutants will accumulate in thesoil with each application of sludge. The risk assessment considers pollutant transport through variousenvironmental exposure pathways, and has the objective of setting maximum pollutant loading limits and minimumsludge quality requirements for cropland application of sewage sludge. EPA's analysis focused on those chemicalsthat are resistant to degradation and may be incorporated into food crops, or animal feed, or ingested by grazinganimals. EPA also considered human exposure that can occur through direct ingestion of sludge-amended soil.This last pathway was assessed by EPA based on the residential use of packaged sludge-derived material whereinfants may ingest the dirt, and it is outside the scope of this report. A general description of a risk assessmentapproach is briefly presented below, after which EPA's specific approach is explained and evaluated.


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General Approach to Risk Assessment

The method for performing a risk assessment, as outlined by the NRC (1983), consists of four steps: (1)hazard identification, (2) dose-response evaluation, (3) exposure evaluation, and (4) characterization of risks.

Hazard Identification

The first step in the risk assessment process—hazard identification—is to determine the nature of the effectsthat may be experienced by a human exposed to an identified pollutant and whether evidence of toxicity existssufficient to warrant a quantitative risk assessment. Data are gathered on a specific pollutant and qualitativelyevaluated based on the type of health effect produced, the conditions of exposure, and the metabolic processes thatgovern pollutant behavior within the human body or other organism studied. It may also be necessary tocharacterize the behavior of the pollutant in the environment. Thus, hazard identification helps to determinewhether it is scientifically appropriate to infer that effects observed under one set of conditions (e.g., inexperimental animals) are likely to occur in other settings (e.g., in human beings), and whether data are adequateto support a quantitative risk assessment. The following two sections discuss how such quantitative assessmentsare conducted.

Dose-Response Assessment

The second step in the risk assessment process is estimating or evaluating the dose-response relationships—what "dose" of a chemical produces a given "response"—for the pollutant under review. Evaluating dose-responsedata involves quantitatively characterizing the connection between exposure to a pollutant (measured in terms ofquantity and duration) and the extent of toxic injury or disease. Most dose-response relationships estimates arebased on animal studies, because even good epidemiological studies rarely have reliable information on humanexposure. In this context, two general approaches to dose-response evaluation are used, depending on whether thehealth effects are based on threshold or nonthreshold characteristics of the pollutant. "Threshold" refers toexposure levels below which no adverse health effects are assumed to occur. Effects that involve altering geneticmaterial (including carcinogenicity and mutagenicity) may take place at very low doses; therefore, they aremodeled with no thresholds. For most other biological effects, it is usually, but not always, assumed that thresholdlevels exist.

Exposure Evaluation

Exposure evaluation estimates environmental concentrations of pollutants. The severity of the exposure isthen assessed by evaluating the nature and size of the population exposed to the pollutant, the route of exposure(i.e., oral, inhalation, or dermal), the extent of exposure


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(concentration times duration), and the circumstances of exposure.

Risk Characterization

In the final phase of a risk assessment, the risk characterization, information on the range of exposures andrisks and on all major uncertainties, along with their influence on the assessment, and presented.

EPA's Risk Assessment Approach

Hazard Identification

EPA initially developed environmental profiles and hazard indices on 50 pollutants that were selected by agroup of experts convened by EPA in 1984 (EPA, 1993). Of those 50 pollutants, 22 (10 metals and 12 organics)were selected, through a screening process, for regulation in the 1989 proposed rule for land application (FederalRegister, 1989). These 22 pollutants are listed in Table 7.3.

After the proposed rule was issued, EPA completed a National Sewage Sludge Survey (NSSS) (EPA, 1990).The NSSS sampled sludge from 209 sewage treatment plants throughout the country to produce national estimatesof concentrations of toxic pollutants in sewage sludge.

Using the NSSS data and information from the risk assessment, EPA conducted a further screening analysisto eliminate from regulation any pollutant that was not present in concentrations that posed a significant publichealth or environmental risk. Based on this screening analysis, 12 organic chemicals were deleted, leaving 10inorganic chemicals for regulation by the Part 503 Sludge Rule. The criteria used to remove organic pollutants fromthe rule is discussed below.

Three screening criteria were used to assess the need for regulating the 12 organic pollutants that were part ofthe original 22 pollutants identified in the proposed rule. If a pollutant satisfied any one of the criteria below, itwas exempted from regulation in Part 503. The three criteria were described as follows:

• The pollutant has been banned for use, has restricted use, or is no longer manufactured for use in theUnited States.

• The pollutant has a low frequency of detection in the sewage sludge (less than 5 percent), based on datafrom the NSSS.

• The concentration of the pollutant in sewage sludge is already low enough that the estimated annualloading to cropland soil would result in an annual pollutant loading rate within allowable risk-basedlevels.

Based on these criteria, EPA exempted all of the organic pollutants under consideration. The pollutant loadingused for the third criterion is based on the quantity of sewage sludge that would be applied at agronomic rates andusing the sludge pollutant concentration equal to the


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TABLE 7.3 Pollutants Selected for Initial Hazard Identification Analysis

Inorganic Chemical Pollutants Organic Chemical Pollutants

Arsenic Aldrin/Dieldrin

Cadmium Benzo(a)Pyrene

Chromium Chlordane

Copper DDT/DDD/DDE

Lead Dimethyl nitrosamine

Mercury Heptachlor

Molybdenum Hexachlorobenzene

Nickel Hexachlorobutadiene

Selenium Lindane

Zinc Polychlorinated biphenyls (PCBs)

Toxaphene

Trichloroethylene

SOURCE: EPA, 1993b.

99th percentile value of the NSSS (EPA, 1993b, Appendix B). Table 7.4 lists the criteria by which eachpollutant was screened.

Exposure Assessment

The exposure assessment analyzed 14 pollutant transport pathways (Table 7.5) in agricultural land applicationof sewage sludge. Of primary relevance to the committee's assessment of human health impacts were the threepathways that involved crop consumption. The other pathways traced effects of digestion of soil on livestock,plants, soil biota, soil biota predators, and human-health. At the end of each pollutant transport pathway, there is anexposed subject who is the receptor of the pollutant. For each pathway, the exposed subject represents the segmentof the exposed population that is most susceptible—the "highly exposed individual" (HEI).

The maximum tolerable exposure for the HEI was set equal to the risk reference dose (RfD) corresponding to arisk level of 10-4 for known carcinogenic chemicals and equal to the recommended daily allowance (RDA) fornon-carcinogenic chemicals. EPA traditionally establishes standards within a range of 1×10-7 to 1×10-4, dependingon the statute, surrounding issues, uncertainties, and information bases. EPA chose a carcinogenic risk target of1×10-4 for the use of sewage sludge in the production of agricultural crops because EPA's analysis did not indicate asignificant aggregate populational carcinogenic risk from this practice, and because of the conservativeassumptions built into the HEI approach (EPA, 1993a).

For the purposes of the Part 503 Sludge Rule, models were developed to determine the maximum amount ofpollutant that could be added to the soil (otherwise known as a "pollutant loading") that would not cause unduerisk. This analysis produced 14 pollutant loadings—one for each pathway—for each of the pollutants evaluated.The smallest value of all pathways was selected as the maximum permissible loading for each pollutant. Thisvalue, termed "cumulative


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TABLE 7.4 Results of Screening Criteria for Organic Pollutants Considered for Part 503 Sludge Regulations

Pollutants Pollutant is Banned inUnited States

Pollutant has < 5% DetectionFrequency in the NSSS

Does Not Exceed RiskAssessment Criteria from99th percentile in NSSS

Aldrin/Dieldrin (total) x x

Benzo(a)Pyrene x

Chlordane x x x

DDT/DDE/DDD (total) x x x

Heptachlor x x x

Hexachlorobenzene x

Hexachlorobutadiene x x

Lindane x x x

N-Nitrosodimethylamine x x

PCBs x

Toxaphene x x x

Trichloroethylene x x

pollutant loading rate," sets the total allowable level of sludge-borne pollutant that can be added to the soiland still maintain an acceptable level of exposure to the HEI from the most sensitive pathway. The analysis treatsall pathways as equal so that adverse effects on livestock animals, plants, and soil biota are weighed equally tothose on humans. In other words, if a limiting pathway for a pollutant is one in which the HEI is a plant, thenumeric limit for the pollutant is more restrictive than necessary to protect a human because the plant is moresensitive than the human. The limiting pathway for each of the 10 pollutants regulated and their correspondingHEIs are listed in Table 7.6. It is important to note that none of the limiting pathways involve the humanconsumption of crops grown in sludge-amended soils.


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TABLE 7.5 Exposure Assessment Pathways

Pathway Numbers Pathway

1 Sludge-soil-plant-human

2 Sludge-soil-plant-home gardener

3 Sludge-soil-child

4 Sludge-soil-plant-animal-human

5 Sludge-soil-animal-human

6 Sludge-soil-plant-animal

7 Sludge-soil-animal

8 Sludge-soil-plant

9 Sludge-soil-soil biota

10 Sludge-soil-soil biota-predator of soil biota

11 Sludge-soil-airborne dust-human

12 Sludge-soil-surface water-fish-human

13 Sludge-soil-air-human

14 Sludge-soil-ground water-human

Risk Characterization

EPA established cumulative pollutant loading rates for 10 inorganic elements (Table 7.7). These ratesrepresent the maximum amount of a pollutant that can be uniformly applied to a hectare of land and still provideacceptable protection to the HEI.

To provide flexibility in applying sludges and to expedite the use of sewage sludge in nonagricultural landapplication, several variations in pollutant loading limits were derived from the risk-based cumulative pollutantloading rates. These alternative limits are described below and include pollutant concentration limits, ceilingconcentration limits for pollutants, and annual pollutant loading rates. Recordkeeping and managementrequirements for sludge will vary depending on which set of limits are used (in addition to any requirement basedon the pathogen levels as earlier discussed).


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TABLE 7.6 Most Limiting Pathway for Pollutants Regulated in CFR Title 40, Parts 503

Pollutant Highly Exposed Individual (HEI) Limiting Pathway Number

Arsenic Sludge eaten by child 3

Cadmium Sludge eaten by child 3

Chromium Phytotoxicity 8

Copper Phytotoxicity 8

Lead Sludge eaten by child 3

Mercury Sludge eaten by child 3

Molybdenum Animal eating feed 6

Nickel Phytotoxicity 8

Selenium Sludge eaten by child 3

Zinc Phytotoxicity 8

Pollutant Concentration Limits To derive pollutant concentration limits, EPA assumes that the life span of aland application site is no more than 100 years and that the annual sludge application rate is less than or equal to10 metric tons/ha (an agronomic rate for a typical sludge that would provide adequate available nitrogen for anumber of crops). In this case, the sludge application rate at a given site will not exceed 1,000 metric tons/ha. Therisk-based, cumulative pollutant loading rate (kg of pollutant/ha for the life span of the application site) is thenuniformly distributed among 1,000 metric tons of sludge/ha, and a maximum permissible pollutant concentration(in kg of pollutant/ton of sludge or in mg of pollutant/kg of sludge) was calculated. This value was then comparedto the 99th percentile concentration value for the pollutant from the NSSS and the more stringent of the two wasdetermined to be the pollutant concentration (EPA, 1993a) as shown in Table 7.8. Given these assumptions, thecumulative pollutant loading rates would not be exceeded in normal agricultural practices and there would be littleneed for oversight except to assure that the sludge quality meets the criteria prior to distribution or application.

In an effort to encourage the continued reduction of pollutant levels in the municipal wastewater stream, EPAdeveloped the concept of ''exceptional quality" sewage sludge. Under this classification, sludges with specified lowlevels of pollutants, termed "pollutant concentration limits" and Class A pathogen levels, can be applied toagricultural land with a minimum of regulation and oversight.

Ceiling Concentration Limits for Sewage Sludge According to EPA's risk assessment, any sewage sludgemay be applied on cropland as long as the cumulative pollutant loading rates are not exceeded. However, somesewage sludges contain unusually high amounts of pollutants that are prone to cause harmful effects when appliedon cropland. EPA established ceiling concentrations to prevent such sewage sludges from being applied oncropland. The ceiling concentration of a pollutant is set at the least stringent of: (1) the 99th percentileconcentration


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TABLE 7.7 Cumulative Pollutant Loading Rates

Pollutant Cumulative Pollutant Loading Rate (kg/ha)

Arsenic 41

Cadmium 39

Chromium1 3,000

Copper 1,500

Lead 300

Mercury 17

Molybdenum1 18

Nickel 420

Selenium 100

Zinc 2,800

1 Above limits have been deleted for chromium (since October 1995) and molybdenum (since February 1994) pending reconsideration byEPA.

Annual pollutant Loading Rates Annual Pollutant Loading Rates (APLR) are used as a managementstrategy to make sure that sludges sold or given away in bags do not exceed the risk-based cumulative pollutantloading rates. This applies to sewage sludges with concentrations that are less than, or equal to, the ceilingconcentrations, but do not meet the pollutant concentrations. The APLR is calculated by assuming the cumulativepollutant loading rates are reached in 20 years of agricultural or residential land applications. These preset annualpollutant loading rates shown in Table 7.8 can not be exceeded.

EVALUATION OF FEDERAL STANDARDS FOR CHEMICAL POLLUTANTS IN SEWAGESLUDGE

The objectives of the Part 503 Sludge Rule are to protect human health and the environment from reasonablyanticipated adverse effect of pollutants in sewage sludge and to encourage the beneficial use of sewage sludge. Ifthe regulation is viewed in this manner, the risk assessment approach used by EPA to establish the numericallimits (cumulative pollutant loading rate) is reasonable. The risk assessment is logical and the exposure analysis isconducted with the best available scientific data. Based on the principles and objectives of the regulation and theapproach used for the rule development, the regulation appears to serve its purpose. The limits set on pollutants ofconcern are sufficient to prevent adverse effects on consumers from food crops or animal products exposed tosludge. This type of regulation provides flexibility for users to develop site-specific land application operations. Ifthe numerical limits on pollutant loadings and associated management practices are followed, cropland applicationof sewage sludge can be practiced without causing harm to public health and the environment. Sludge generators,appliers, and regulatory agencies must ensure that agronomic rates are followed and that numerical limits are notexceeded.


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TABLE 7.8 Ceiling Concentrations, Pollutant Concentration, and Annual Pollutant Loading Rates

Pollutant Ceiling Concentration Limits(mg/kg)

Pollutant Concentration Limits(mg/kg)

Annual Pollutant LoadingRates (kg/ha/yr)

Arsenic 75 41 2.0

Cadmium 85 39 1.9

Chromium1 3,000 1,200 150.0

Copper 4,300 1,500 75.0

Lead 840 300 15.0

Mercury 57 17 0.85

Molybdenum1 75 18 0.90

Nickel 420 420 21.0

Selenium1 100 36 5.0

Zinc 7,500 2,800 140.0

1 Above limits for chromium and molybdenum (except for ceiling concentration) have been deleted, and the pollutant concentration limitshave been revised for selenium.

In the course of reviewing the rule-making process, the Committee noted some inconsistencies in how thenumeric limits were developed. A discussion of these inconsistencies follows. While the inconsistencies do notaffect food safety, they point to areas that need attention from EPA in its follow-up assessments to improveconfidence in the regulation. EPA is scheduled to update Part 503 in the near future and will be addressingpollutants not currently regulated in "Round Two" of Part 503.

Justification for Exempting Organic Pollutants From Regulation Should be Confirmed

Initially, EPA identified 12 organic pollutants for regulation in 1989. Following a review of public commentson the proposed rule, the Agency undertook a screening exercise to re-evaluate the need to regulate these 12organic pollutants. The exercise resulted in no organic chemicals being regulated under the final rule promulgatedin 1993. The application of the screening criteria, however, leads to concern with certain organic pollutants, whoseconcentration in sewage sludge may exceed the risk-based limits for these pollutants.

The screening criteria compared the APLR, based upon the NSSS's 99th percentile


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concentration of each pollutant, to the annual pollutant loading concentration calculated by the Part 503 exposureassessment. If the 99th percentile concentration of a pollutant resulted in an annual pollutant loading rate less thanthe loading calculated through the risk-based exposure assessment, EPA saw little justification in regulating thepollutant.

However, there are four pollutants (PCBs, benzo(a)pyrene, hexachlorobenzene and N-Nitrosodimethylamine)whose 99th percentile concentrations resulted in calculated APLRs higher than those calculated by the exposureassessment. When calculating the APLR, EPA used 7 metric tons as the annual whole sludge application rate foragricultural land. However, in its development of the APLR for trace elements, 10 metric tons was used. Therationale for using a lower application for calculating trace organic loading rates is based on their decomposition inthe soil.

Table 7.9 shows how various percentile concentrations of pollutants from the NSSS compare to theconcentrations of pollutants that would have been allowed using the EPA's exposure assessment. This table showsthat the 99th percentile concentration of benzo(a)pyrene, hexachlorobenzene, N-Nitrosodimethylamine and PCBsare higher than the concentrations that would have been allowed by the APLR determined through the riskassessment. In other words, should these pollutants be detected in sludges at levels approaching the 99thpercentile, they could pose more of a risk than the exposure assessment would have considered acceptable. For thethree pollutants other than PCBs, this may be a rare occurrence considering that the NSSS detected thesepollutants in less than 5 percent of the sludges sampled. But 19 percent of the sludges had detectable levels ofPCBs; thus, those sludges with particularly high concentrations of PCBs may be posing some risk that the riskassessment would consider unacceptable.

However, at the 90th and 50th percentile concentrations of PCBs, few sludges should have total PCBconcentrations above the exposure assessment value of 4.6 mg/kg (see Table 7.9). The 90th percentileconcentration is 1.2 mg/kg and the 50th percentile concentration is 0.2 mg/kg (the 98th percentile concentration,not shown, is 2.8 mg/kg). Therefore, it is unlikely that most sludges would have levels above 4.6 mg/kg. Theconcern is then limited to sludges that might have concentrations of total PCBs higher than 4.6 mg/kg; this shouldbe a small percentage of all sludges in the United States.

For N-Nitrosodimethylamine the APLR calculation using the 50th percentile concentration is above theexposure assessment APLR. This pollutant was eliminated because it was detected in less than 5 percent of thesamples. However, in those samples where it was detected, the concentrations may be high enough to be ofconcern.

This entire analysis on organic chemicals depends on the integrity of the NSSS. One criticism of the NSSSwas its use of wet weight detection methods and conversion of these to dry weight concentrations. Because of thisinconsistency in sampling, the limits of detection may vary by as much as two or more orders of magnitude for thesame chemical among sludges from different POTWs. As a result, the frequency of a chemical's detection may beunderestimated. When the limit of detection value is used in determining the mean and standard deviation of achemical's concentration, these measures may become unreliable. This is more of a problem for toxic organicchemicals than for trace elements because many of the toxic organic chemicals occur infrequently and neardetection limits in sewage sludge, whereas trace elements are almost always detected. To improve the quality ofthe data set, EPA plans to repeat the Survey in the near future. A second NSSS is needed to provide moredefinitive documentation


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to show whether or not concentrations of organic chemicals are within the range of concentrations that do notpose a risk to human health or the environment. If the NSSS does not support this conclusion, EPA should developlimits for those organics which exceed safe levels.

APLRs May Cause Maximum Permissible Loading Limits to be Exceeded

Sewage sludges that are marketed and distributed in bags are used primarily as soil amendments inlandscaping or home gardening. Although "bagged" sludge products are not used routinely for this purpose, theamount of sewage sludge applied each time they are used could be large. In the rule-making process, EPA justifiedallowing sludges that exceeded the "exceptional quality" criteria of the lowest pollutant concentration limits (seetable 7.8) to qualify for marketing and distribution. EPA argued that this approach is justified because pollutantinputs exceeding the calculated annual pollutant loading rate (APLR), should they ever occur, would result in littleadditional pollutant uptake by plants (Chaney and Ryan, 1992). While this may be an adequate technicaljustification for agricultural use, allowing sludge of less than the highest quality to be used by the general publicopens the door for exceeding regulatory limits, and may undermine the intent of the Part 503 Sludge Rule andpublic confidence in the law.

Food Safety is not Likely to be Affected by the Regulations

In the risk assessment conducted by EPA, 14 exposure pathways were employed. Among them, ninepathways involve human HEI (pathways 1, 2, 3, 4, 5, 11, 12, 13, and 14 in Table 7.5), three of which are directlyrelated to production of human food crops on sludge-amended agricultural land. These are "sludge-soil-plant-human" (pathways 1), "sludge-soil-plant-animal-human" (pathway 4), and "sludge-soil-animal-human" (pathway5). In the Part 503 Sludge Rule, the final numerical limit of a pollutant is the lowest cumulative pollutant loadingof all 14 exposure pathways. Because other, nonfood-chain pathways resulted in lower pollutant limits, the finalcumulative pollutant loading for 10 chemical pollutants currently being regulated are all significantly lower thanany of the limits that would be derived from the human food-chain exposure pathways. Table 7.10 shows the finalcumulative pollutant loading rates in kg/ha for the 10 regulated pollutants and what the limits would have been ifthey were based on the food-chain exposure pathways.

In some cases, the food crop production pathway limits were not determined because the oral reference dose(RfD) or the recommended dietary allowance (RDA) for the pollutant did not exist owing to the fact that uptake ofthe particular constituent is inconsequential, or because the food exposure pathway is extremely small compared toexposure from other sources. In this comparison, the margin of safety provided by the current regulation rangesfrom 6 to over 1,700 times greater than the final cumulative pollutant loading adopted by EPA.

Table 7.11 shows a corresponding comparison for organic pollutants that were not regulated. In this case, theresults have all been converted to annual pollutant loading rates (kg/ha/yr) rather than the cumulative pollutantloading rates shown in Table 7.10 for trace elements


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TABLE 7.10 Final Cumulative Pollutant Loading Rates vs. the Maximum Pollutant Loading Rate Calculated from Food-Chain Exposure Pathways

Pollutant Cumulative Pollutant Loading Rate (kg/ha) Maximum Permissible Pollutant Loading Rate (kg/ha)

Pathway 1 Pathway 4 Pathway 5

Arsenic 41 6,700 NA* NA

Cadmium 39 610 1,600 68,000

Chromium 3,000 NA NA NA

Copper 1,500 NA NA NA

Lead 300 NA NA NA

Mercury 17 180 1,500 24,000

Molybdenum 18 NA NA NA

Nickel 420 63,000 NA NA

Selenium 100 14,000 15,000 13,000

Zinc 2,800 16,000 150,000 2,200,000

* NA: not applicable because (1) plant uptake is inconsequential, or (2) food exposure route to humans is extremely small compared toexposure from other sources.SOURCE: EPA, 1993b

(see footnote, p. 140). Table 7.11 shows that the most limiting, risk-based pollutant rate used by EPA toscreen these chemicals was, in most cases, based on the risk of consuming animal products from animals directlygrazing on sludge-amended fields (pathway 5). As discussed in Chapter 6, organic pollutants in sludge are notreadily absorbed by plants. To be of significance to humans consuming crops grown with sludge, the soilconcentrations of organic pollutants would have to be orders of magnitude higher than those for the grazinganimal pathways. Consuming the meat of animals grazed on sludge-amended fields is a potential concern becauseanimals may accumulate certain pollutants in the kidneys and liver (as discussed in Chapter 6). As discussedearlier and shown in Table 7.9, four organic pollutants are of potential concern because their 99th percentileconcentration in the NSSS exceeded the risk-based limits for the pollutant. Of these four, the grazing animalpathway was used to set the risk-based limit for hexachlorobenzene and PCBs. Hexachlorobenzene occurred at low(less than 5 percent) frequency in the survey, but PCBs had a detection level of 19 percent; however, the concernis limited to sludges that might have total concentrations of PCBs higher than 4.6 mg/kg, which should also be asmall percentage of all sludges in the United States. (see Table 7.12 for a listing of the limiting pathways).

REGULATIONS AND GUIDANCE FOR AGRICULTURAL USE OF MUNICIPALWASTEWATER

In the United States, there is a long history of using municipal wastewater for crop irrigation.


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TABLE 7.11 Maximum Permissible Organic Pollutant Loading Rates Calculated from Food-Chain Exposure Pathways

Pollutant Most Limiting Pollutant Rate (kg/ha/yr)

Maximum Permissible Pollutant Loading Rate (kg/ha/yr)

Pathway 1 Pathway 4 Pathway 5b

Aldrin/Dieldrin 0.03 (5) 2.8a 0.2a 0.03

Benzo(a)Pyrene 0.15 (3) 23 NAc NA

Chlorodane 0.9 (3) 34 360a 23

DDT/DDD/DDE 1.2 (12) 560 48 1.5

Dimethylnitrosoamine 0.02 (3) 87 NA NA

Heptachlor 0.7 (5) 990 110 0.07

Hexachlorobenzene 0.3 (5) 320 48 0.3

Hexachlorobutadiene 6 (3) 43,300 NA 6

Lindane 0.8 (3) 2,300 1,500 1.4

PCBs 0.05 (5) 37 4.3 0.05

Toxaphene 0.10 (5) 2,800 120 0.1

Trichloroethylene 100 (3) 220,000 NA NA

a Values shown for the Most Limiting Pollutant Rate are obtained from EPA, 1993b in Table 5.4–5.6, pp. 5–436, of the Technical SupportDocument of the Part 503 Regulation. These values represent the smallest of the reference annual pollutant application rates (or "RPa"measured in kg/ha/yr) for the organic pollutant. Where an RPa was not directly available, it was derived from the reference cumulativeapplication rates (or "RPc" measured in kg/ha, which are used in Table 7-10) by assuming a life span of the application site of 100 years.Therefore, the RPa would be 1/100th of RPc. Alternately, an RPa was derived from the reference concentration of a pollutant in sewagesludge (or "RSC" measured in µg/g) by assuming an annual sewage sludge application rate of 10 metric tons/ha. The number inparenthesis indicates the pathway from which the most limiting pollutant rate is derived.b All values converted from concentration of pollutant in sewage sludge (mg/kg) with the assumption of sewage sludge application rate at10 metric tons/ha/yr.c NA: not applicable because (1) plant uptake is inconsequential, or (2) food exposure route to humans is extremely small compared toexposure from other sources.SOURCE: EPA, 1993b

Although the practice has not been extensive, reclaiming municipal wastewater for crop irrigation is well-established in some parts of the country. Over the years, federal agencies have not exercised direct regulatoryauthority over either wastewater irrigation or other type of effluent reuse, except through provisions in theNational Pollutant Discharge Elimination System permit system which regulates the discharge of treatedwastewater effluents. In practice, wastewater irrigation is normally treated as a community-wide environmentalsanitation and public work improvement project that should undergo rigorous facility planning and engineeringevaluation (EPA, 1981). The technical merit, market feasibility, and public health risks of each potential projectshould be carefully reviewed by many agencies before it is implemented. This


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TABLE 7.12 Limiting Pathways for Organic Chemical Pollutants Evaluated in the Development of The Part 503 SludgeRule

Pollutant Highly Exposed Individual (HEI) Limiting Pathway Number

Aldrin Eating animal fat/milk 5

Dieldrin Eating animal fat/milk 5

Benzo(a)Pyrene Sludge eaten by child 3

Chlordane Sludge eaten by child 3

DDT/DDD/DDE Eating fish 12

Dimethylnitrosamine Sludge eaten by child 3

Heptachlor Eating animal fat/milk 5

Hexachlorobenzene Eating animal fat/milk 5

Hexachlorobutadiene Eating animal fat/milk 5

Lindane Sludge eaten by child 3

PCBs Eating animal fat/milk 5

Toxaphene Eating animal fat/milk 5

Trichlororethylene Sludge eaten by child 3

is usually done and there have been no reported incidents in the United States of food contamination and/orwater pollution caused by applying treated wastewater effluents to cropland.

The public health is protected by adequate and reliable treatment of the reclaimed water as well as siterestrictions associated with the degree of treatment. In the United States, both the level of wastewater treatmentand the microbiological requirements for agricultural reuse vary from state to state. By 1992, at least 19 States hadset regulations or guidelines for the use of reclaimed water on food crops.

Recently the EPA published guidelines for the reuse of wastewater in a number of applications, including usein agriculture (EPA, 1992a). Those recommended criteria that are pertinent to infectious disease transmissionthrough agricultural application are summarized in Table 7.13. Reclaimed water applied to most food crops,particularly those that can be eaten uncooked, should be processed at least through secondary treatment followedby filtration and adequate disinfection.

Evolution of Regulations Governing Irrigation with Treated Municipal Wastewater

In many respects, California has been a pioneer in reclaiming and reuse of municipal wastewater. Thewastewater irrigation-related regulations in California can therefore be used as a model for examining regulatorydevelopment. The California Water Code (State of California, 1987) declares that "the people of the state have aprimary interest in the development of facilities to reclaim water containing waste to supplement existing surfaceand underground water supplies and to assist in meeting the future water requirement of the state" (Cal. WaterCode, Section 13510). The statute further declares that "the use of potable domestic water for nonpotable uses,including, but not limited to, cemeteries, golf courses, parks, highway land-scaped


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TABLE 7.13 Summary of EPA Guidelines for Reclaimed Water Reuse in Agriculture

Type of reuse Treatment Required Water quality

Food crops not commercially processed SecondaryFiltrationDisinfection

<2.2 fecal Coliform/100mL1mg/L Cl2 residual after 30 min. contact time(minimum)Turbidity ` 2NTU` 10mg/L BOD

Food crops commercially processed includingorchards and vineyards

SecondaryDisinfection

`200 fecal coliform/100mL1mg/L Cl2 residual after 30 min. contact time(minimum)` 30mg/L BOD` 30mg/L SS

Nonfood crops pasture, fodder, fiber and seed SecondaryDisinfection

` 200 fecal coliform/100mL1mg/L Cl2 residual after 30 min. contact time(minimum)` 30mg/L BOD` 30mg/L SS

areas, and industrial and irrigation uses, is a waste or an unreasonable use of the water with in the meaning of …the California Constitution if reclaimed water is available.…" (Cal. Water Code, Section 13550). These policydeclarations culminated in a mandate that "the State Department of Health Services shall establish statewidereclamation criteria for each type of use of reclaimed water where such use involves the protection of publichealth" (Cal. Water Code, Section 13521). In California, wastewater reclamation and reuse is an integral part ofthe water resource management plan. The provisions of Reclamation Criteria of California (Department of HealthServices, 1993) reflect the legislative intent. They are conducive to water reuse and are enacted to protect publichealth when reclaimed water is used.

Long before the statutes were official, domestic wastewater was used in crop irrigation (Ward and Ongerth,1970). In 1910, at least 35 communities in California operated sewage farms to dispose of raw sewage or septictank effluents. In 1918, the California Board of Health adopted regulations governing the use of sewage forirrigation purposes. It prohibited the use of raw sewage, septic tank effluents, and other similar wastewater forirrigation of vegetables that would be consumed uncooked by people. The regulation permitted the use of untreatedwastewater for irrigating crops that would be cooked before consumption, provided that a 30-day or longer waitingperiod was observed prior to harvest. It also permitted the use of reclaimed water for fruit and nut trees and meloncrops if the products did not come into direct contact with the wastewater. For the next 75 years, the regulationscontinued to evolve in response to new experience in wastewater use, new wastewater treatment technology, andas the demand for reclaimed wastewater rose.

In 1933, the regulation was revised to allow the use of well-oxidized, nonputrescible, and reliably disinfectedor filtered effluents for irrigation of vegetable crops for raw consumption.


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Requirements were established for the finished water's coliform counts and the treatment plant operations.Subsequently, a more comprehensive regulation for the use of reclaimed water for irrigation and recreationalimpoundments was adopted in 1968 to accommodate the increasing population and volume of reclaimed wateravailable for reuse. The new standards specified levels of wastewater treatment required and coliform density offinished water for various type of uses. The need to insure wastewater treatment reliability and to limit publicaccess to the application site was documented based on the data of several field investigations. In 1975, regulatoryprovisions were added to guarantee wastewater treatment reliability and to limit public access to the applicationsite. Since it inception, the Reclamation Criteria (California Department of Health Services, 1993) has beenrevised several times. However, the technical requirements for crop irrigation remained the same as written in1975.

General Description of the State Regulations

As the demand for reclaimed wastewater for crop irrigation spread across the nation, many states enactedregulations or developed guidelines to govern its use. Recently, EPA (1992a) published guidelines for water reuseincluding the use of reclaimed water in agriculture in the United States. The conditions for use of reclaimed waterfor irrigating food and nonfood crops in 18 and 35 states, respectively were summarized.

The Reclamation Criteria of California (California Department of Public Health Services, 1993) have been amodel for reclaimed water regulations for many states. The primary health concerns targeted have been the risk ofpathogen and chemical pollutant exposure to workers involved in irrigation projects, to residents near awastewater irrigation site, and to consumers of food produced from wastewater-irrigated fields. Regulations havefocused on infectious disease risks by establishing the following:

• the level of wastewater treatment required (primary treatment, secondary treatment, oxidized, filtered,coagulated, disinfected, etc.);

• the upper limits for selected water quality parameters to insure wastewater treat-ment reliability (maximumBOD, total suspended solids, chlorine residual, turbidity, indicator organisms concentrations permitted,and pH range, etc.), and on-line chlorine residual and turbidity;

• treatment reliability provisions;• site management practices that prevent workers and residents from being exposed to applied water and

contaminated soils at the application site (providing setback distance, limiting public and worker access,posting warning signs, cross-connection prevention, hydraulic loading rate, etc.); and

• water management practices that minimize contamination of crops (specifying method of irrigation and/or types of crops permitted, requiring waiting period for crop harvesting or animal grazing, maximumwater application rate, etc.)

Regulations define the conditions necessary to minimize human exposure to pathogens. This is accomplishedby specifying the degree of treatment the wastewater receives, by specifying


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time and environmental conditions to reduce pathogen survival prior to human contact, and by restricting certainfood crops depending on the level of reclaimed water quality. There are usually backup technical requirements inthese state regulations such as simultaneous specification of wastewater treatment levels to minimize presence ofpathogens, provision of setback distance to prevent direct contact with pathogens, and waiting period requirementafter irrigation to reduce pathogen survival.

Five of the 18 states that permit reclaimed water for irrigation of produce crops require advanced wastewatertreatment (e.g., oxidation, clarification, coagulation, filtration, and disinfection). To ensure the consistency oftreatment performance, the total coliform (or fecal coliform) density of finished water is required to be less than orequal to 2.2 per 100 milliliters. Under such a circumstance, the reclaimed water is considered to be essentially freeof pathogens for nonpotable reuse purposes. Other requirements such as setback distance, waiting period, andrestricted site access are, in this case, not necessary.

At the other end of the spectrum, primary effluents may be permitted to irrigate food crops for processing ifrequirements are met to protect workers and nearby residents and to prevent water pollution. Human exposure topathogens is controlled by factors other than pathogen density in the wastewater effluents. The deficiency in onefactor may be mitigated by more stringent requirements of other factors. For example, in Utah, food crops may beirrigated by secondary effluents with total coliform density up to 2000/100 ml (30-day average), provided sprayirrigation is not used. In this case, the risk of exposure to pathogens is reduced by preventing the water fromcoming into direct contact with the food crop.

If reclaimed water is used to irrigate nonfood crops or animal food crops, the risk of exposure to pathogens isconsiderably smaller than with vegetables produced for raw consumption by humans. Therefore, restrictions onwastewater treatment levels and operational reliability usually are more relaxed for nonfood crops than are thoserequired for irrigating human-consumed food crops. Effluents from oxidation ponds, primary treatment, andsecondary treatment are all acceptable under various circumstances. But the other requirements such as setbackdistance and site access usually remained the same or become more stringent for the protection of workers andnearby residents. Many states (15 of the 35 states that permitted reclaimed wastewater for nonfood crop irrigationin 1992) either: (1) ban the used of lower-quality treated wastewater on pasture, (2) require disinfection whenirrigating pastures for milking animals, or (3) require an extended waiting period before animals are allowed onfields irrigated with lower-quality wastewater effluents.

So far, trace chemical contaminants in treated municipal wastewater have not been targeted by Stateregulations or EPA guidelines for reclaimed water because their concentrations in wastewater receiving a minimumof secondary treatment are comparable to conventional sources of irrigation water (see Chapter 4). Source controlof industrial inputs, conventional secondary treatment, and advanced treatment are relied on to reduce effluentconcentrations of chemical pollutants to levels that meet current irrigation water quality criteria (e.g., Wescot andAyers, 1985) for chemicals that are potentially harmful to crop production or to ground water contamination. Thisassumption appears justified if industrial pretreatment programs are rigorously enforced by municipalities andwastewater is properly treated. In such case, it is possible to produce reclaimed wastewater that meets the highestrequired water quality standard for irrigation of food crops and with trace element and organic chemicalconcentrations that are


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lower than the maximum contamination levels of the National Primary Drinking Water Standard (Crook et al.,1990). If the concentrations of chemical pollutants tabulated in Table 7.14 are typical for reclaimed water, theannual pollutant inputs to the soil through reclaimed water irrigation will be small and will be balanced or out-balanced by the output through crop absorption (see Chapter 4 for details). In this manner, toxic chemicals andtrace elements are not expected to accumulate in soils irrigated with reclaimed water to levels that are harmful tohumans.

Adequacy of Current Regulations for Reclaimed Water

California's Water Code defines the Reclamation Criteria as ''levels of constituents of reclaimed water, whichwill result in reclaimed water safe from the standpoint of public health, for the uses to be made" (Cal. Water Code,Section 13520). Early on, state regulatory agencies recognized that numerous pollutants are present in reclaimedwater, and it is impractical, if not impossible, to track all of them. Besides, there is little epidemiological data todefine the dose-response relationships. Defining "levels of constituents of reclaimed wastewater" suitable forvarious uses is difficult if the epidemiological data for quantitative dose-response evaluation are not available. As aresult, regulations for reclaimed wastewater irrigation always rely on the capability of wastewater treatment andsite management to accomplish the goal of public health protection.

While the public health safety record for reclaimed water irrigation has been excellent, there are littleepidemiological data to support or refute the currently regulated levels (Crook, 1978; 1982). For developingcountries, recent research in epidemiology indicates that the public health risks resulting from crop irrigation withtreated municipal wastewater are overestimated, and that the United States guideline may be "unjustifiablyrestrictive, particularly with respect of bacterial pathogens" (World Health Organization, 1989).

Are current regulations for reclaimed water adequate to protect human health? The answer to this questiondoes not lie in the regulations alone. Over the past century, the environmental sanitation practice of collecting,treating, and disposing municipal wastewater has been instrumental in improving the public health. Over time, anintegrated infrastructure has evolved to regulate, plan, and implement the monumental task of handling municipalwastewater day-in and day-out. This system is vertically integrated with the environmental protection andpollution control authorities at the federal level, water quality and public health authorities at the state level, andthe environmental sanitation authorities at the local level. The nation is also horizontally connected acrosspolitical boundaries by special service agencies that have responsibilities for collecting, treating and disposingwastewater. Within the framework of this infrastructure, policies are made; funds are generated and appropriated,regulations are enacted; and physical plants are planned, built, and maintained. The common objective cuttingacross the entire infrastructure are to safeguard public health and to prevent environmental pollution.


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TABLE 7.14 Concentration of Trace Elements and Toxic Organic Chemicals in Selected Treated Effluents in California

Pollutant Unit San Jose Creek Whittier Narrow Pomona NPDWSa

Arsenic mg/l 0.005 0.004 <0.004 0.05

Aluminum mg/l <0.06 <00 <0.08 1.0

Barium mg/l 0.06 0.04 0.04 1.0

Cadmium mg/l NDb ND ND 0.01

Chromium mg/l <0.02 <0.03 <0.03 0.05

Lead mg/l ND ND <0.05 0.05

Manganese mg/l <0.02 <0.01 <0.01 0.05

Mercury mg/l <0.0003 ND <0.0001 0.002

Selenium mg/l <0.001 0.007 <0.004 0.01

Silver mg/l <0.005 ND <0.005 0.05

Lindane µg/l ND ND ND 4

Endrin µg/l ND ND ND 0.2

Toxaphene µg/l ND ND ND 5

Methoxychlor µg/l ND ND ND 100

2,4-D µg/l ND ND ND 100

2,4,5-D µg/l <01 ND ND 10

Turbidity NTUb (silica scale) 1.6 1.6 1.0 2

Total Coliform No./100 ml <1 <1 <1 2.2

a National Primary drinking water standardsb ND denotes the constituent was not detected in the specimen.SOURCE: Crook et al., 1990.


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The interdependency and interlinking of the components provide check-and-balance and technicalredundancy to ensure that integrity will not be breached and that the well-being of the public is not threatened bypollutants and pathogens in the wastewater (see additional discussion in Chapter 8 on Other GovernmentRegulations).

When viewed in this manner, the practice of irrigation with reclaimed water is not a monolithic event.Instead, it is merely one component of this integrated wastewater handling, treatment, and disposal infrastructureerected to protect public health and prevent environmental pollution. Whether crop irrigation can be safelyadministered is therefore interdependent on whether other components of the system are performing up toexpectation. The current reclaimed wastewater irrigations regulations take full advantage of the advances inwastewater treatment technology to deliver water of appropriate quality. Again, the record has been a successfulone.

If the integrity of the infrastructure is maintained, it is reasonable to assume that reclamation of wastewaterfor food crop irrigation will continue to be practiced safely. Because of the checks and balances and technicalredundancy offered by the system, the likelihood of failure is small and, if failure occurs, it is likely to be promptlydetected and corrected. Although the risk from trace chemical contaminants in reclaimed water applied to foodcrops has not been quantified, it is likely that such use presents little additional risk since the levels of tracechemical contaminants in reclaimed water are normally within accepted guidelines that have been developed forirrigation with conventional sources of irrigation water.

SUMMARY

Pathogen Regulations for Sludge

In the United States, the Part 503 Sludge Rule is the current management strategy for the application ofsludge to land. At the present state of our knowledge, this rule appears to be, with one possible exception, adequatefor the protection of the public from the transmission of waste associated pathogens. The possible exception is thepotential that the prescribed waiting period between the application of Class B sludge and animal grazing may notbe adequate to prevent the transmission of tapeworm to grazing cattle.

Toxic Chemicals Regulations for Sludge

The Part 503 Sludge Rule was developed with the intent to encourage beneficial use of sewage sludge. Usingrisk-assessment-based calculations, the regulation specifies numerical limits for chemical pollutant loading rateswithin which the sewage sludge may be safely applied on cropland. The regulation has a sound conceptual basisfor protecting public health and encouraging beneficial use of sewage sludge.

In terms of trace elements, sewage sludge that is applied according to the pollutant loading rates specified inPart 503 should not affect the safety of the nation's food supply. The pollutant loading rates are set by themaximum permissible loading rates of nonfood-chain


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pathways, which are 6 to 1,700 times smaller than the maximum permissible pollutant rates according to food-chain related exposure pathways.

No organics are currently regulated by Part 503. Most toxic organic compounds found in municipal sewagesludges exist at concentrations well below those considered to pose a risk to human health or the environment.However, benzo(a)pyrene, hexachlorobenzene, and N-nitrosodimethylamine, detected in less than 5 percent of thesludge samples analyzed in the NSSS, occurred at concentrations above the 99th percentile ceiling concentrationused by EPA in setting an acceptable risk. Total PCBs may be of concern because they occurred at a higherfrequency of detection (19 percent), but only a small fraction is expected to exceed risk-based limits. Some of thesample preparation and analytical methods used in the NSSS for measuring concentration of toxic organiccompounds in sludge were not sufficiently sensitive to show whether or not toxic organic compounds werepresent sludges at levels that would pose a threat to human and animal health. Therefore, a second survey shouldbe conducted with better sampling methods to determine concentrations of toxic organic compounds, and thosewhich exceed risk-based limits should be regulated.

Sludges allowed for marketing and distribution to the public have the potential to cause maximumpermissible pollutant limits to be exceeded. While not a food safety issue, this has the potential to undermine theintent of Part 503.

Regulations for Effluent Irrigation

State regulations governing reclaimed wastewater for crop irrigation rely on wastewater treatment and sitemanagement to (1) minimize the presence of pathogens, (2) prevent workers, residents, and consumers from directcontact with wastewater or wastewater-contaminated soils and crops, and (3) minimize the opportunity forpathogen survival after water application. They do not address trace chemical contaminants. The requirementsstipulated in these regulations, such as type of wastewater treatment, set-back distance, waiting period, coliformdensity of finished water, etc., vary considerably. The variation is caused by the many factors that control the riskof exposure. The deficiency in one factor is often offset by more stringent requirements for other factors.

The current requirements of reclaimed wastewater for crop irrigation were not derived by risk-based analysisand are not supported or refuted by actual epidemiological data. They are based on experience in wastewatertreatment and reclaimed wastewater crop irrigation operations. The checks and balances and technicalredundancies provided by today's wastewater treatment infrastructure seem to provide an ample margin of safety.


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REFERENCES

California Department of Health Services. 1993. Proposed Regulation. California code of Regulations, Title 22, Division 4, Chapter 3. Officeof Drinking Water. Berkeley: California Department of Health Services.

California Water Code. 1994. Porter-Cologne Water Quality Control Act. California Water Code, Division 7. Compiled by the State WaterResources Control Board, Sacramento, California.

Chaney, R. L. and J. A. Ryan. 1992. Regulating Residual Management Practices. Water Environ. & Technol. 4(4):36–41.Chang, A. C., A. L. Page, and T. Asano. 1993. Developing Human Health-Related Chemical Guidelines for Reclaimed Wastewater and

Sewage sludge Applications. Community Water Supply and Sanitation Unit, Division of Environmental Health. Geneva,Switzerland: World Health Organization 113 pp.

Cooper, R. C. and J. L. Riggs. 1994. Status of pathogen analytical techniques applicable to biosolids analysis. P. 13 in The Management ofWater And Wastewater Solids for The 21st. Century—Proceedings of WEF Specialty Conference, June, 1994. Water EnvironmentFederation, Alexandria, Vir.

Crook, J. 1978. Health aspects of water reuse in California. J. Environ. Div. ASCE 104(EE4):601–610———. 1982. Wastewater reuse in California—regulations and rationale. Pp. 263–281 in Individual Onsite Wastewater Systems. L. Waldworf

and J. L. Evans, eds. Proceedings, the Eighth National Conference, National Sanitation Foundation, Ann Arbor, Michigan.Crook, J., T. Asano, and M. Nellor. 1990. Groundwater recharge with reclaimed water in California. Water Environ. Technol. 2:42–49.EPA. 1981. Process design manual for land application of municipal wastewater. EPA 625/181-013. Cincinnati, Ohio: U.S. Environmental

Protection Agency, Center for Environmental Research Information.———. 1990. National Sewage Sludge Survey: Availability of information and data, and anticipated impacts on proposed regulations.

Proposal Rule 40 CFR Part 503. Federal Register 55:47210–47283.———. 1992a. Manual Guidelines for Water Reuse. EPA/625/R-92/004. Washington, D.C.: U.S. Environmental Protection Agency. 245 pp.———. 1992b. Statistical Support Documentation for the 40 CFR, Part 503 Final Standards for the Use and Disposal of Sewage Sludge, Final

Report November 11, 1992. Vols. I and II. U.S. Environmental Protection Agency, Office of Science and Technology Engineeringand Analysis. Washington, D.C.: U.S. Environmental Protection Agency.

———. 1993a. Standards for the Use And Disposal of Sewage Sludge; Final Rules, 40 CFR Parts 257, 403, and 503. Federal Register 58(32):9248–9415. February 19, 1993.


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———. 1993b. Technical Support Documents for 40 CFR Part 503. Land Application of Sewage Sludge, Vol. IPB93-11075; Land Applicationof Sewage Sludge, Vol. IIPB93-110583, Appendices A-L; Pathogen and Vector Attraction Reduction in Sewage SludgePB93-110609; Human Health Risk Assessment for Use and Disposal of Sewage Sludge, Benefits of Regulation PB93-111540; TheRegulatory Impact Analysis PB93-110625. Springfield, Virginia: National Technical Information Service.

Federal Register. 1989. 54:5746. February 6.Feachem, R. G., D. J. Bradley, H. Garelick, and D. D. Mara. 1983. Sanitation and Disease. New York: John Wiley and Sons. 501 pp.Isole, B., N. C. Kyvsgaard, P. Nansen, and S. A. Henriksen. 1991. A Study On The Survival Of Taenia sargenata Eggs In Soil In Denmark.

Acta. Vet. Scand. 31(2);153.McGrath, S. P., A. C. Chang, A. L. Page, and E. Witter. 1994. Land application of sewage sludge: scientific perspectives of heavy metal

loading limits in Europe and the United States. Environ. Rev. 2(1):108–118.National Research Council. 1983. Risk Assessment and Management: Framework for Decision Making. Washington, D.C.: National Research

Council .Ward, P. C. and H. J. Ongerth. 1970. Reclaimed wastewater quality, the public health viewpoint. Pp 31–36 in Proceedings of Wastewater

Reclamation and Reuse Workshop, Berkeley, CA June 25–27, 1970. University of California, Sanitary Engineering ResearchLaboratory and Sanitary Engineering Graduate Programs at Berkeley, Davis, and Irvine.

Wescot, D. W. and R. S. Ayers. 1985. Irrigation water quality criteria in Irrigation with Reclaimed Municipal Wastewater. A GuidanceManual, G. Pettygrove and T. Asano, eds. Chelsea, Mich.: Lewis Publishers.

World Health Organization. 1989. Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture. Final report submitted toCommunity and Water Supply Sanitation Unit. Washington, D.C.: World Health Organization.

Yanko, W. A. 1988. Occurrence of pathogens in distribution and marketing municipal sludges EPA/600/1-78/014. Washington, D.C., U.S.Environmental Protection Agency, Office of Water.

Yanko, W. A., A. S. Walker, J. L. Jackson, L. L. Libao, and A. L. Garcia. 1995. Enumerating Salmonella in biosolids for compliance withpathogen regulations. Waster Environ. Res. (67)3:364.


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8

Economic, Legal, and Institutional Issues

Earlier chapters have made the case that agricultural use of wastewater effluent and sludge, whenappropriately treated (Chapter 3) and applied according to prevailing regulations or guidelines (Chapter 7), can bepracticed satisfactorily with respect to public health (Chapters 5 and 6), crop production, and environmentalconcerns (Chapters 2 and 4). This chapter discusses some of the economic issues, "residual risks", and otherregulatory matters facing various interested parties involved in implementation. Residual risks are risks perceivedby crop producers, food processors, and the public (such as local nuisance, food consumer safety, and agribusinessliability as examples) that persist despite federal (for sludge) and state (for effluent) regulatory safeguards. Thischapter begins with an examination of the economic incentives driving beneficial reuse from the perspectives ofsociety, the municipal wastewater treatment utility (also known as the "publicly-owned treatment works" orPOTW), the landowner or farmer, and the food processor. Discussion then turns to key concerns about residualrisks for the various groups. The chapter concludes with a review of the regulatory framework for food safety andenvironmental protection and its capacity to address the residual risks. Thus, the chapter provides an assessment ofthe adequacy of existing economic, legal, and regulatory mechanisms for addressing these outstanding concerns.

ECONOMIC INCENTIVES FOR LAND APPLICATION OF TREATED MUNICIPALWASTEWATER AND SLUDGE

Interest in reclaiming treated wastewater effluents is being driven by two major factors. One is the increasingcost of water supplies in many metropolitan areas, especially the arid western United States. For example, thewholesale cost for fresh water in Southern California can exceed $800/acre-foot ($2.45/1000 gal), depending onthe treatment requirements and the distance from the source; by comparison, most types of water reclamation costmuch less than $750/acre foot (Water Reuse Association of California, 1993). The second factor is the growingvolume of wastewater (as shown in Figure 1.1) and the increasing cost of complying with water pollution controlregulations governing wastewater discharges into the environment. This is especially apparent where excessnutrients from discharged wastewaters can cause water quality

ECONOMIC, LEGAL, AND INSTITUTIONAL ISSUES 151

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problems. For example, the sensitivity of aquatic habitats in Florida prompted the City of Orlando and OrangeCounty to develop, as an alternative to surface water discharge, the CONSERV II program which combineswastewater irrigation on citrus groves with ground water recharge (D'Angelo et al., 1985). In St. Petersberg,Florida, water reclamation also began based on disposal requirements; however, the reclaimed water now has agreater value as a substitute for scarce potable water drawn from aquifers 50 miles away. Driven by economic andenvironmental concerns, and encouraged by the similarity of treated wastewater effluents to irrigation water, theuse of reclaimed wastewater for agricultural irrigation is potentially competitive with other sources of water andcan be a cost-effective alternative to wastewater discharge in selected parts of the country.

Generation of sewage sludge likewise has been steadily increasing in this country as a result of highertreatment levels and greater quantities of wastewater from continued population growth. Municipalities have usedvarious options for the disposal of sewage sludge, including landfill, incineration and ash disposal, oceandumping, and land application. The public reaction in 1988 to the appearance of medical wastes along New Jerseyshores (Spector, 1992) led to the enactment of the Ocean Dumping Act (P.L. 100-68) that included a ban on oceandisposal of sewage sludge. The limited capacity of sanitary landfills is quickly exhausted, and communities arenot providing for new landfills. Air quality requirements for incineration plants are increasingly stringent. Becauseof the these restrictions, the Bureau for Clean Water, which handles waste-water treatment for New York City,must spend approximately $800/ton to ship its sludge out of state (Wagner, 1994). As society has continues toreevaluate and regulate disposal options, agricultural use of sludge is becoming an increasingly attractive optionbecause of its low cost and because of the fertilizer and soil amendment properties of sludge (see Chapter 4).

The following sections describe economic issues relating to the use of both reclaimed treated wastewatereffluents and treated sewage sludge from the perspectives of the various parties affected by agricultural useprojects. The specific costs and benefits are site specific; thus, no generic assessment of the tradeoffs is possible.The focus of this study is on the use of treated effluents and treated sludge in the production of food crops, and nocomparative assessment is made of the economics of other use or disposal alternatives for sludge and wastewater.

POTW Economic Perspectives

The alternatives available to POTWs for treatment and ultimate release of wastewater and sludge into theenvironment are circumscribed by the Clean Water Act and by state and federal regulations for solid wastedisposal. Thus, POTWs face the problem of deciding which of the available options for treatment and disposal ofthe sludge and wastewater are most appropriate and cost effective for their particular circumstances.

Cost-effectiveness analysis (Baumol and Oates, 1988) is an analytic tool commonly used by POTWs inchoosing among available options for wastewater management. The major cost components of conventionalwastewater systems include collection, treatment, wastewater discharge, and disposal of sludge (Milliken, 1990).Direct cost factors include the characteristics


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of the wastewater, type of treatment, size of facility, location, and type of sludge treatment, and ultimate disposalor reuse method. The costs of performing these functions include capital costs for building the facility, and annualoperation and maintenance costs. The capital costs are generally amortized over the life of the facility in order toarrive at an annualized capital cost.

Most POTWs in the United States are required to perform a minimum of secondary treatment (seeChapter 3), and this can be considered as a baseline for POTWs in considering a change in their function fromproviding wastewater disposal to reclamation. Only the additional level of treatment and other costs associatedwith changing to water reclamation options need to be considered. However, in some areas (e.g., Florida), landapplication of wastewater may allow for lower levels and costs of treatment compared to surface water disposaldue to the advance treatment that would be required to remove nutrients from effluents prior to discharge intosensitive surface waters.

The Florida Department of Environmental Regulation (1991) issued guidelines for the economic evaluationof implementing water reuse projects. The feasibility guidelines require the comparison of the net present valuesof alternatives (including the current practice) over a 20-year period. Capital construction costs are to include thecost of wastewater collection and treatment, and reclaimed water transmission to the point of delivery for the enduser, plus reasonable levels of related costs such as engineering, legal service, and administration. Annualoperation and maintenance costs must also be calculated for each alternative. Effluent irrigation alternativesgenerally require additional costs for effluent collection, advanced treatment, transportation to reuse sites,irrigation management, and water storage.

State requirements for wastewater effluent quality vary depending on the type of crop and irrigation method.The U.S. Environmental Protection Agency suggested guidelines (EPA, 1992) for water reuse include secondarytreatment plus disinfection for nonfood crops, commercially processed food crops, and surface irrigation oforchards and vineyards. Secondary treatment plus filtration and disinfection is suggested for irrigation of foodcrops that are not commercially processed and that could be eaten raw.

An analysis of the cost of supplying reclaimed water to agriculture was recently completed in the Tampa,Florida area (Hazen and Sawyer, 1994). Treatment included filtration and chlorination of secondary treatedeffluent. Additional costs included 2.5 million gal of storage for every 10 million gal/day of capacity andtransmission costs of $.35/1000 gal. Total costs of supplying reclaimed water to agriculture were estimated torange from $.70 to $.90 per 1,000 gal (approximately $225 to $300 per acre-foot). For comparison purposes,farmers typically pump water directly from the aquifer at a cost of approximately $.10 to $.15 per 1,000 gal. Waterobtained from the water utility service is at the same order of magnitude at $.82 to $1.06 per 1000 gal. The cost tothe farmer will depend on whether reclaimed water is used to comply with water quality regulations, which is thecase in Orlando and Tallahassee, or whether reclaimed water is used to offset short supplies of water, as in Tampa.Incentives to the farmers will not be needed in water-short areas, but may be needed in other areas where waterquality concerns drive the reclamation effort.

There are a variety of economic approaches and market alternatives that POTWs may use to offset currentand future costs of supplying reclaimed water. If water reclamation results in a reduction in the demand for currentpotable water—i.e., if agriculture is drawing on an existing or potential potable water supply—the reductionshould be valued at the average rate


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charged for potable water in order to determine the benefits of the reclaimed water. If the reclaimed water is sold,then revenue from the sale of reclaimed water may be available to offset reclamation costs. Finally, the POTWmay decide to own and manage agricultural land for land disposal of wastewater effluent. In this case, revenuefrom the sale of commodities produced may be available to help offset reclamation costs. For example, the city ofTallahassee, Florida owns a 1,720 acre agricultural operation that accommodates an average of 12 to 18 milliongal/day of effluent (Roberts and Bidak, 1994).

The implementation of any wastewater reclamation plan may allow the community to avoid or delay the costof expanding potable water supply systems, and potential cost savings should be included in the economic analysisof water reclamation alternatives. A study by the Irvine Ranch Water District in California showed that, while the1987 wholesale cost of treated fresh water (at $230/acre-foot) was less that the cost for water reclamation (at$303/acre-foot), it was projected that wholesale water costs would rise to $449/acre-foot (calculated in 1987dollars) by the year 2000 because of rising demand and system expansion (Young et al., 1987). Water reclamationwould allow the community to avoid the need for water supply expansion and thus save $146/acre-foot.

Sludge handling is an important aspect of POTW operations. Evans and Filman (1988) indicate that sludgehandling costs accounted for an average of 47 percent of the total treatment plant costs for four large treatmentplants in Ontario, Canada. Some of the processes that are used include thickening, dewatering, drying,conditioning and transportation (as described in Chapter 3). The EPA handbook, Estimating Sludge ManagementCosts (EPA, 1985) describes a number of different unit processes that can be used to achieve each of these varioussteps and provides generic comparative cost curves as well as specific algorithms for calculating unit costs for eachprocess. However, the large number of processes that can variously be combined into any particular sludgemanagement train, and the site-specific nature of the costs of implementing many of these processes, preventsmeaningful generic cost comparisons. For example, the Evans and Filman (1988) study compared sludge handlingcosts for four treatment plants with different sludge handling processes, but all subject to identical effluentdisposal requirements. Total sludge processing costs ranged from $266/ton to $925/ton depending upon thespecific unit processes employed for sludge treatment.

Treatment procedures and quality criteria to be met for various types of end uses or disposal of sludge arespecified in the Standards for the Use and Disposal of Sewage Sludge (or "Part 503 Sludge Rule", EPA, 1993).Effective pollutant source control and industrial pretreatment programs will be required to meet EPA requirementsfor high-quality pollutant concentration limits. Specific processes are necessary to meet the Class A pathogenreduction levels. The advantage of meeting these higher-quality sludge requirements is that the sludge can beapplied to agricultural land with lower costs for regulatory compliance.

Sludge transportation can be a significant cost of land application. Transportation costs depend primarily onthe quantity of water in the sludge and the distance transported. As described in Chapter 3, sludge volume can bereduced by thickening, dewatering, conditioning, and drying. Dick and Hasit (1981) discuss the tradeoff betweenadditional treatment costs to reduce sludge volume and the savings in transportation costs. This tradeoff dependsupon the distance the sludge is to be transported, the mode of transportation, and the cost of reducing sludgevolume. The Madison, Wisconsin Metrogro Program determined that agricultural use


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of liquid sludge was the least expensive alternative since they had access to over 30,000 acres of farmland within a20 mi radius of the POTW (Taylor and Northouse, 1992).

Comparisons of sludge management alternatives, should include the potential, if any, of revenue frombeneficial land applications. Sludge contains nutrients and organic matter that can substitute in part or whole forcommercial fertilizers or soil amendments (e.g, see Table 2.2). The Madison Metrogro program charges farmers$7.50/acre of sludge applied (Taylor and Northouse, 1992). Their application rates are determined by the mostlimiting factor, either crop nitrogen requirements or regulatory levels for metals. However, income generated fromthis fee covers only 1–2 percent of total program cost. The fee charged to farmers exists primarily to reinforce theconcept that sludge is a beneficial product rather than a waste. Since 1979, Metrogro has recycled 139,000 tons ofdry solids, with a total fertilizer value of over $2 million. Farmers' demand to participate in the program farexceeds the District's ability to supply sludge and is indicative of the local value of sludge as a soil amendmentproduct.

Farm Economics of Treated Wastewater and Sludge Use

A farmer considering the use of reclaimed wastewater or sludge will initially have several concerns, includingthe potential health risks to family and employees, potential toxic effects on the plants, long-term detrimentalchanges in physical or chemical properties of the soil that may affect crop production, the potential liabilityassociated with the sale or consumption of crops grown using wastewater and sludges, and the fear of liability forcontamination of the land with hazardous wastes. Sewage sludge is not listed as a hazardous waste under theResource Conservation and Recovery Act (RCRA) unless it exhibits characteristics that make it a hazardous wasteand prevent its beneficial use (EPA, 1993). This last issue has been of concern to farm bank lenders who have afinancial interest in the value of the land. These concerns, which are reviewed in the next section under ''ManagingResidual Risks," will have to be addressed before growers will even consider whether using wastewater or sludgeis profitable or not.

Only after these concerns are adequately addressed will farm economics come into play. Treated wastewaterand sludge provide inputs (water and nutrients) to agriculture. The demand for these inputs will depend on theirrelative contribution to production—also known as "marginal productivity"—and the price of the crop. The costand availability of substitute sources of fertilizer or irrigation water provide ceilings to the price the farmer willpay for the nutrients and water in the treated effluent. In general, the greater the marginal productivity and thehigher the price of the product, the higher will be the marginal value of the crop and the willingness-to-pay forwater or nutrients. The agricultural marginal value for irrigation water is quite variable. In the early 1980s, thecongressional Office of Technology Assessment (1983) estimated that the values of water for irrigated agricultureranged from $9/acre-foot for pasture to $103/acre-foot for vegetables (these 1983 estimates would be about 50percent larger in 1995 dollars.) Boggess et al. (1993) provide a comprehensive discussion of the economics ofwater use in agriculture. Moore, et al. (1985) provide a detailed assessment of the on-farm economics of reclaimedwastewater irrigation in California (also see the discussion of irrigation water value in Chapter 2).

The value of the nutrients will depend primarily on the relative levels of the various nutrients


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in the water and the nutrient requirements of the crop. Estimates for the CONSERV II project in Florida place thetotal value of nutrients in the reclaimed water at $100 to $250 per acre per year (D'Angelo et al. 1985), which isequal to or exceeds current farm fertilizer costs of approximately $100–$120 per acre (Muraro et al., 1994).Because fertilizer costs generally do not exceed 10 percent of total farm costs, and because its application throughirrigation is not as easily controlled as through conventional fertilizers, it is not likely that farmers will place muchvalue on the fertilizer benefits of reclaimed water. Additionally, nutrients in wastewater effluent may present aproblem for some crops at certain stages of growth as discussed in Chapter 4.

Whether or not reclaimed wastewater can be marketed to agriculture also depends on the cost and availabilityof reclaimed water relative to other sources of irrigation water. Supply considerations include seasonality andstorage as well as the on-site delivered cost of reclaimed water. Florida, for example, receives an average of 50 in.of rain per year, but irrigation is critical for the production of high-value crops. This is due to the low water-holding capacity of the soils, the high evapotranspiration rates, and irregular timing of rainfall events. Estimatesfor the CONSERV II project indicate that growers save from $75 to $150/acre/year in irrigation costs (D'Angeloet al. 1985). However, this estimate is based on the total amount of water sent to the growers in the CONSERV IIprogram, which is in excess of what they would normally use. Typical irrigation costs for growers pumpingground water in the areas are estimated at $30–$70 per acre (Muraro et al., 1994). Nevertheless, growers in theCONSERV II project have not been required to pay for the new water supply because water sources in the area(from ground water) are inexpensive and easily accessible, and more importantly, because the CONSERV IIproject was initiated by the county and city to avoid the higher cost of complying with the water qualityrequirements for discharge, not because water is a scarce resource.

Where effluent irrigation projects are motivated by disposal, farmers may resist applying water to oblige theutility. In addition, farmers will be concerned about whether sufficient water will be available during periods ofpeak need, or whether or not they will be required to take water in excess of their needs. These concerns wereworked out in the CONSERV II project in Florida (D'Angelo et al. 1985). The citrus grower participants in theproject have agreements that require them to take a total of approximately 50 in. of water per year even thoughtypical irrigation rates are only 12 to 24 in. per year. The contract allows the grower to refuse delivery ofscheduled quantities of water for a limited number of periods each year. In addition, the City of Orlando andOrange County agreed to provide additional wells to the farmers to insure adequate water to protect crops fromfreezing, since the supply of treated effluents would be inadequate during these peak use events. Inaccommodating the seasonal nature of water demand, the POTW developed a series of rapid infiltration basins forground water recharge. This option allows the POTW to divert excess effluent to the recharge basins when cropirrigation needs are low.

Sewage sludge has value to the farmer for its nutrient content and as a soil conditioner. The market demandfor sludge will depend on the marginal productivity of sludge, the cost of alternative sources of nutrients or soilamendments, and regulatory and permitting costs. The marginal productivity of sludge varies with the soil andtype of crop. Crop yields will show greater responses to sludge applications on those soils which are poor innutrients and organic matter (see Chapter 4). Likewise, certain crops require greater quantities of nutrients. Thus,


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from a strictly economic perspective, the willingness-to-pay for sludge should be positively related to the crop'snutrient requirements and inversely related to the inherent fertility of the soil.

The availability of low-cost commercial fertilizers will generally be a limiting factor on farmers'willingness-to-pay for sludge. The nitrogen content of sludge usually ranges between 1 and 4 percent, whichwould be worth roughly $6–$24 per dry ton, given 1994 prices for commercial bulk nitrogen fertilizers. Othernutrients in sludge, such as phosphorus, may also contribute to its value (EPA, 1994). Metrogro, the sewage sludgeagricultural use program in Wisconsin, estimates an average fertilizer value of $15/dry ton of sludge (Taylor andNorthouse, 1992). Farmers will also be concerned about the mix of nutrients in the sludge relative to the crop'sneeds. While sewage sludge can supply all crop nutrients if applied according to nitrogen requirements, fertilizerapplication rates are not as easily controlled as with commercial products and supplemental fertilizer may beneeded in some instances to meet the crop's requirements (see Chapter 4).

Other economic considerations for the farmer include the cost of applying sludge and the additionalmonitoring, recordkeeping, and management required by federal, state, and local regulations. However, some orall of these costs are typically incurred by the contractor and/or POTW. Conversely, the POTW may choose ahigher level of sludge treatment and thus reduce other regulatory requirements. Treatment and regulatory costsincurred by the POTW, may be passed on to the public in the form of higher rates. Regulatory and somemonitoring costs are generally incurred by public agencies, and thus, taxpayers. Other management and monitoringcosts are borne directly by sludge handlers and users.

In some cases, the costs associated with monitoring, handling, and recordkeeping requirements may equal orexceed the direct economic benefits of land application, even though land application may be the environmentallypreferable and the most cost-effective alternative from society's point of view (i.e. when all direct, indirect andsocial costs and benefits are considered). In these cases, it may be necessary and appropriate for the POTW tosubsidize private sludge handlers and users in order to offset these costs. However, care should be taken to insurethat the subsidy payments are properly structured and don't create incentives for "dumping" or application ofsludge at rates exceeding appropriate agronomic levels. Subsidies also can obscure beneficial value and create theillusion that sludge is a waste product that farmers have to be paid to accept. As earlier mentioned, the MadisonMetrogro program solved this problem by having the POTW incur the costs for transporting the sludge to the farmsite, injecting it into the ground, and perform the monitoring recordkeeping. Farmers pay $7.50/acre, which paysonly a small portion of program costs, but helps to reinforce the notion that sludge is beneficial product.

Benefits of crop productivity and cost savings have been documented in individual cases. In westernWashington state, the Wegner farm has been applying sludge from Spokane since 1988 at 4.5 dry tons/acre/year(Logsdon, 1993). The sludge, in the form of wet cake, is incorporated into the soil before the growing season.Wegner reports 35 percent increases in yields (and increased protein content) of barley and wheat and a fertilizersavings of $12 to $25 per acre.


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Food Processor Perspectives

To survive financially, food processors and retailers must have a demand for their food products and fill iteconomically. Thus, anything that may affect the demand for their products of their cost of production is ofconcern. The use of wastewater and sludge may reduce the cost to the buyers of raw food products if growers areable to reduce their costs, increase productivity, and sell their crops at a more competitive price. However, theimpact of using treated effluents and sludge on the cost of producing food crops is likely to be quite small for tworeasons. First, as discussed in Chapter 2, the extent of wastewater irrigation in agriculture represents much lessthan one percent of irrigated crops and is not likely to increase, due to the limited availability of cropland close towastewater treatment plants, and the competing (mostly urban) uses for reclaimed water in those areas wherereclaimed water has value. For sludge, even if all of the sewage sludge produced in the United States were land-applied to agriculture, these inputs would provide nutrients for less than 2 percent of cropland. Secondly, the valueof sludge and wastewater as fertilizer will be no more than 10 percent of the total costs of farm production. As aresult of these scale effects, land application is not likely to have significant impact on the average cost of growingfood. Finally, from a farmer's perspective, the potential problems associated with sludge and wastewater couldquickly outweigh the benefits. These factors will limit any cost savings that could be passed on to food processorsas an incentive to purchase from farms that apply wastewater and sludge.

The potential liabilities or costs associated with the use of treated effluents and sludge for food processorsstem from the public perception that adverse health effects could result (for example, the concern over Alarpesticide in apples, bovine growth hormones in milk, or conversely, the popularity of foods labeled as "organic").Nevertheless, public perception does not necessarily depend on objective, scientific evidence. As discussed inChapter 7, negative human health effects from the consumption of food crops are unlikely under the Part 503Sludge Rule or under state regulations for effluent irrigation of crops. Still, food processors and retailers areparticularly concerned about potential liability for health risks attributed to the consumption of food grown withthe use of treated wastewater effluents or treated sludge. They require evidence to convince them that all aspectsof the process are being carefully managed according to the regulations and guidelines, and that there is adequateoversight and enforcement.

MANAGING RESIDUAL RISKS

It is important to consider management and program oversight before embarking on reuse alternatives forboth wastewater and sludge. Acceptance of the practice by the local community and farmers, and the public'sconfidence and trust in the public utility is a prerequisite to program success. As discussed in the followingsections, concerns over public health, food safety, neighborhood nuisances, community land values, marketabilityof crops, sustainability of farmland, and the reliability of safe farming practices are important implementationissues. These all need to be adequately addressed, and will impose new burdens on agencies and the private partiesinvolved. The capacity of the POTW to undertake an agricultural-use project in


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this context is an important threshold consideration. Florida, for example, limits water reuse projects to largerPOTWs because smaller facilities may lack the staff and finances to do an adequate job (Ferraro, 1994).

Residual Risks

The purpose of EPA's Part 503 Sludge Rule and state regulations on wastewater irrigation are to assure safeuse of sludge and wastewater in agriculture. In addition, numerous other regulatory programs are designed toprotect the environment from agricultural contamination and protect consumers from adulterated foods (asdiscussed later in the chapter).

Nevertheless, many concerns have been raised about the "residual risks" of using sludge and wastewater inagriculture—those risks that may persist despite the regulatory safeguards. These concerns include potential risksto:

• the health of persons and livestock who consume foods produced with treated sludge and treatedwastewater effluents;

the health of agricultural workers and other persons on agricultural sites where sludge and wastewaterare used;

• the health of persons who consume ground water, surface water, or fish or shellfish from areas wheresludge and wastewater are used;

• the quality of life and value of property of nearby residents; and• the quality of natural resources, such as agricultural soil, rivers, wetlands, ground water, flora, and fauna.

While only the first concern—that of health effects from food crops—is the main focus of this report, theimplementation of agricultural use programs for wastewater effluents and sewage sludge will ultimately depend onthe degree to which all of these concerns are addressed. Business risks and burdens also arise from these concernsabout residual risks, making farmers and food processors reluctant to produce and process foods grown with theaid of sludge and wastewater, and making retailers reluctant to sell these foods. The business risks may outweighany benefits that farmers gain by using these materials. For example, community concerns can lead to enactmentof local or state regulations that prohibit agricultural use of sludge or wastewater in certain regions, or impose newand costly technical safeguards and monitoring duties. On a national scale, consumer concerns about the safety ofcrops grown with sludge or wastewater can stimulate consumer and retailer boycotts of certain products, newlabeling requirements (which tend to stigmatize such products), and new food inspection and reportingprocedures.

In addition, several banks that finance farmers in the northeast have been concerned about whether repeatedapplications of sludge containing toxic substances (such as cadmium and lead), even at the levels set by EPA'sPart 503 Sludge Rule, could potentially put a farm at risk of becoming a hazardous waste site and create cleanupliabilities. These lenders have an interest in protecting the value of the farmland that secures their loans, and areconcerned about whether they would be designated as "responsible parties" liable for the cleanup costs. Afterstudying


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the issue, the Farm Credit Institutions of the Northeast (an organization of farm credit banks) determined thatassurances may be needed to cover the economic risk. They proposed that farmers seeking their loans throughmortgage financing should make sure that the POTW that provides them with sludge will indemnify them in theevent of hazardous waste liabilities that result from application of the sludge (Benbrook and Allbee, 1994).

Other business risks pervade the sensitive markets for food products. Farmers and food processors areaffected when a court or agency finds that its food product is contaminated and has caused, or is likely to cause,personal injury to consumers or livestock. Such determinations can rapidly lead to economic losses in the form ofagency impoundment and destruction of the products, regulatory penalties, tort liability in the form ofcompensatory and punitive damages for personal injuries, and contract liability for breach of product warranties.

But the major business risk for farmers and food processors in such instances is stigmatization of the productand its source. This leads to loss of customer confidence, choice of competing products, and loss of market shareon regional and even national scales. Even if contamination or injury causation is unproved, these consequencesmay occur because widespread media coverage, speculations, or allegations may be enough to make retailers andconsumers reject the product.

Thus, public concerns about residual risks create business risks and militate against agricultural use of sludgeand reclaimed water despite the regulatory safeguards provided by federal and state agencies. Proponents of sludgeand wastewater use must, therefore, address the sources of such public concerns if they are to achieve their goals.

Public Concerns to be Addressed

Public concerns fall into several categories. One category consists of "nuisance" risks to community qualityof life and property values, such as odors, traffic, and the attraction of vermin to sludge application sites. Anothercategory of concern has to do with protection of nearby natural resources of high value, such as wellwater, otherwater supplies, and fish. It is common experience that such resources are highly vulnerable to agriculturalcontamination (e.g., from pesticides). Consequently, local opposition to specific projects and general publicconcern are not uncommon, especially where there has been a limited history of relatively safe use (seeZimmerman et al., 1991; Gigliotti, 1991; Business Publishers, Inc., 1993). Some states may limit the ability oflocal authority to place restrictions on practices that are allowed by the state. Small community governments have alimited capacity to deal with all the issues that are raised, and local residents may feel threatened. For example, theresidents of New Harmony, New Jersey have been plagued by odors from an adjacent farm, which appears to be adumping ground for both municipal sludge and food processor wastes (Markle, 1994). Also concerned aboutenvironmental impacts, the New Harmony residents have been repeatedly frustrated in their attempts to bring theirconcerns to the attention of state regulators who permit the farm for application of in-state and out-of-state sludge.

Elsewhere, these types of public concerns have already led to enactment of local ordinances banning orrestricting sludge application, as in Merced County, California (Sludge Newsletter, 1993). Such ordinances havesurvived legal challenges where they are not preempted


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by federal law and are within the broad scope of the "police power" possessed by state and local governments. Forexample, a federal district court ruled that a Virginia county ordinance completely banning the land application ofsewage sludge as a method of disposal is not preempted by federal law and does not interfere with interstatecommerce (Welch v. Rappahannock County Board of Supervisors, DC WSVA, No. 94-002-C, May 24, 1995).

The POTW and cognizant officials must provide the public with assurances that meet such concerns. Studieshave shown the importance of bringing the public into the decision-making process at an early stage for thispurpose, and the importance of informing the public of the results. Necessary assurances may include ademonstration of stringent self-regulation and monitoring by state and local agencies; reliable management andreporting by the POTW, contractors, and farmers; and vigilant enforcement by regulatory agencies. In particular,there must be assurance that the beneficial use program has credible means of preventing nuisance risks and harmto the nearby resources of high value. Visible demonstrations have been shown to be effective in making peopleaware and comfortable with reuse projects. Moreover, it is unlikely that insurance, liability, indemnification, orother compensation for harms would be sufficient to offset such public concerns.

In Chapter 7, questions were raised about EPA's approach to screening toxic organic pollutants and theirexemption from regulation. While the committee concluded that these organic pollutants in sludge were not likelyto present a risk to consumers of food crops, public concerns have been raised by the fact that even a small percentof sludges have concentrations of certain pollutants (e.g., PCBs) that exceed a risk-based limit of acceptability. Inaddition, it is difficult for the public to understand that the application of sludge on cropland is safe when oceandumping of sludge is prohibited even though the major reason for prohibiting ocean disposal of sewage sludge hadto do with excess nutrient loads on marine ecosystems rather than toxic pollutants or beach safety concerns. Otherquestions have been raised about the safety of wastewater effluents and sludge. A recent report by the GeneralAccounting Office (1994) dealt with the presence of radioactive material entering sewage treatment plants and thelack of regulatory action on this issue. This committee has not delved into that particular issue or other issuesinvolving the quality of municipal wastewater, but it is possible that such concerns will arise when a POTW electsto recycle wastewater or sludge on cropland. Addressing such concerns about sludge requires convincing scientificanalysis showing that adequate safeguards are being applied.

Finally, some of the concerns about the use of sludge in agriculture are based on a lack of confidence in theability of federal and state government to adequately enforce regulations that have been enacted to safeguardhealth and the environment. In addition, farm management is not regulated by the Part 503 Sludge Rule. As withother fertilizers or soil amendments, farmers are expected to use good farming practices that prevent the nutrientsin sludge from causing water quality problems. When using sludge of lower sanitary quality ("Class B" sludge),the Part 503 Sludge Rule requires a statement by farmers that they understand and have complied with restrictionson the type of crops used and necessary waiting times prior to harvest. The public health impact of using Class Bsludge on farms is protected if the farmer follows these restrictions and guidelines (see discussion in Chapter 7).However, the Part 503 Sludge Rule does not regulate potential water-quality impacts that are broadly covered bythe Clean Water Act (EPA, 1993, and see discussion later in this Chapter), and farm management is not


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easily enforced. These public concerns must also be addressed by state and local authorities.

Risk Management: Private Sector

Private sector forces have the potential to deter inappropriate behavior by the parties involved in theproduction, treatment, and use of sludge and wastewater. These include: (1) common law liability, (2) marketforces, and (3) voluntary self regulation. Taken together, the private sector forces and regulatory programs havethe potential to minimize the residual risks and possibly to dispel public concerns.

Common Law Liability

As with many products, liabilities for personal injury and property damage can arise at various stages in thelife cycles of treated sludge and treated effluents, such as when the product is put to use, when it becomes acomponent of other products (crops and derivative foods), when the subsequent products are consumed as foods byconsumers, and when the product wastes are disposed. In the event that the primary or derivative products or theirwastes are found to cause harm to consumer health, property, or resources during any part of the life cycle, it islikely that liability, in the form of compensatory and punitive damages, will be imposed by the courts inaccordance with the tort and product liability doctrines of state common law. In the case of environmentalproblems, regulatory penalties and cleanup costs may also be imposed.

For example, if harm befalls a consumer of a product that was produced with sludge or wastewater, thefarmer or food processor may incur liability for negligence if it is shown that they failed to meet the prevailingstandard of care in their field of activity. Parties who produce or sell food products are held to a particularly highstandard of care and are thereby especially vulnerable to negligence actions. They are even more vulnerable inthose states that hold that failure to meet a regulatory requirement constitutes negligence per se, obviating the needfor the victim to prove negligent conduct.

Personal injury claims by food consumers may also be brought against farmers or food processors under astate's strict product liability doctrine for selling a "defective product." According to this doctrine, a defectiveproduct is one that is unreasonably dangerous due to faulty design or manufacture (e.g. due to a breakdown inPOTW treatment, in farm management practice, or in food processor quality control) or due to inadequatewarnings of latent risks of the product or inadequate instructions for its safe use. In such cases, farmers, foodprocessors, and even POTWs are particularly vulnerable to liability because the victim need establish only that theproduct was defective and that the defect caused the injury, and is not required to prove negligent conduct, a moredifficult task.

Liability may also arise from nuisance claims by owners of neighboring property, such as when sludge orwastewater contaminates or otherwise impairs (e.g. via odors) their use and enjoyment of their property. Liabilitycan arise from claims of breach of contract warranty (express or implied warranty) regarding the fitness of theproduct for use in the production of food or as a constituent part of a processed food for human or animalconsumption.


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Finally, claims of inverse condemnation may be brought against POTWs by farmers whose land iscontaminated by improperly treated sludge or wastewater provided by the POTW. Such a claim could be based onthe constitutional doctrine that prohibits governmental "taking" of private property without just compensation. Aninverse condemnation action would be a possible means of securing compensation for property damage from agovernmental organization (such as a POTW) despite laws in many states which establish governmental immunityfrom tort claims.

As a result, farmers and food processors face potential liability for compensatory and punitive damages underthe common law for a broad range of harms that might occur throughout the life cycles of treated sludge andwastewater. Liability should make these parties act responsibly when engaging in agricultural and food productionpractices that use sludge and wastewater. Insurance and indemnification agreements are helpful and may cover orshift liability to other parties; however, these devices are incapable of reducing the stigma and loss of customersthat usually follows from liability claims. The economic consequences of high-profile accusations can be moresevere than the liability itself.

Thus far, the risk of common law liability has been too high for some food processors and some farmers, andhas contributed to their reluctance to use sludge and wastewater as part of food crop production for processing. Alonger term view is that liability potential will induce care, and in the case at hand, will not be viewed as adeterrent to sludge or wastewater use when the parties have sufficient confidence that their practices will not incurliability. Development of such practices is aided by regulatory requirements. It is also aided by voluntary self-regulation, as discussed below.

Market Forces

When treated wastewater is reclaimed to meet water supply demand in regions where natural water supply isinadequate, the treated effluent has economic value. This value should support investment by the POTW seller inreliable treatment systems, and other expenditures to minimize risks, such as proper application and use, by thefarmer who purchases it. Accordingly, risks in this "strong market" scenario are likely to be adequately controlled.

A different scenario arises when agricultural use of wastewater or sludge is being promoted by the POTW inorder to facilitate disposal and reduce disposal costs, as in cases where environmental constraints limit otherdisposal options and there is no local demand for the wastewater. In such cases, the wastewater is withouteconomic value and its subsequent disposal by means of agricultural use may have negative economic valuebecause of the expenditures that will still be required for its treatment and safe use. If POTW cost avoidance is therationale, farmers, community residents and others may be concerned about the POTW's responsibilities andrequire special assurances.

Once sludge or wastewater has been used to grow crops, market forces arise that may act to reassureconsumers about the safety of food products. As discussed earlier, farmers and food processors operate in safety-conscious markets. Thus, once a farmer has accepted sludge or wastewater, the market forces should act to assurethat appropriate farm management practices are followed, and that effective quality control methods will be usedby food processors,


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since both parties have so much at stake. Experience of the marketability of crops grown with reclaimed water inCalifornia with food brokers and buyers for food chains show no reason for separate labeling, low business risk,and a good track record with no incidents (The Marketing Aim, 1983). However, in other cases, this market forcehas been perceived as both a cost burden and business risk, which many farmers and food processors are unwillingto assume. Voluntary self-regulation of sludge application by farmers and food processors, in the form of codes ofconduct and self-imposed management practices, could help to mitigate negative market force effects, as discussedbelow.

Voluntary Self-Regulation

Self-regulatory programs are being developed in many business sectors to help companies comply withregulations, avoid liability, and to help customers use products safely. Although company conformance to suchguidance is voluntary, failure to conform marks a company as one that does not meet the prevailing industrystandard of care or its state of the art for managing risks. Conformance to the standard is promoted by the potentialof adverse economic consequences of nonconformance (e.g, loss of customer confidence, heightened potential fornegligence liability, and regulatory action in the event of an injurious outcome).

Food processors currently protect themselves by having an official position of not purchasing food fromfarms that use sludge or wastewater (National Food Processors Association, 1993). However, food processors andfarmers have the opportunity, through their various associations, to develop new guidance for quality control andfarm management practices that can reduce the residual risks of using treated sludge and wastewater. Suchguidance, if followed, could have the further effects of mitigating public concerns about regulatory inadequacies,and mitigating business concerns about liability.

Successful self-regulatory programs are available as models. They include private sector training andcertification programs, self-auditing, independent third party evaluation of performance, and specific practices forrisk management.

Although such self-regulation and codes of conduct are developed within the private sector, governmentagencies such as EPA and U.S. Food and Drug Administration could provide encouragement and generic guidanceto assure their proper design. The agencies could also provide various incentives for such self-regulation, such ascooperative agreements, which lessen regulatory actions, inspection, and enforcement in accordance with theeffectiveness of self-regulation.

OTHER, RELATED GOVERNMENT REGULATIONS

The part 503 Sludge Rule and state regulations for agricultural irrigation with treated effluent work within amuch larger framework of regulations. To assure that adequate institutional controls address residual risk, it isimportant to understand the relationships between the various regulatory programs other than those that dealstrictly with agricultural use of municipal wastewater and sludge. In this regard it is important to keep in mind twoconcepts.


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First, all of society's wastes eventually become reassimilated within our environment, and therefore possess apotential for adverse impact to humans. Second, existing institutional programs and other factors, such as liability,have thus far mitigated most risks from the use of treated wastewater and sewage sludge, and, in the case ofsludge, these programs are now being supplemented by beneficial use management options in the Part 503 SludgeRule.

This section of the report illustrates the relationship between federal programs to show how the seeminglyunrelated programs combine to achieve a protective strategy that mitigates potential residual risks associated withmunicipal wastewater and sludge management.

Toxic Waste Segregation, Waste Collection, and Treatment

Figure 8.1 illustrates some of the processes in the wastewater and sludge life cycle generally addressed byfederal and state environmental regulations. Management of municipal wastewater begins before treatment throughsource control and pollution prevention programs. Residential sources are managed through separation of stormwater from sanitary wastewaters and by public education that promotes responsible behavior towards hazardousmaterial disposal. Pollution from industrial wastewater sources is regulated through limits on certain toxicsubstances entering the municipal wastewater (40 CFR 129), and specific industrial effluent quality standardsassigned to particular types of industries (40 CFR 400–471). Many industries also employ voluntary programs torecycle or recover materials in industrial processes that would otherwise pollute the waste stream. Additionalprotection is indirectly provided by the Toxic Substances Control Act (40 CFR 700–799), which describes specificuse requirements for many chemical substances. Wastewaters from residential and industrial sources are conductedthrough the common, public sewers. Discharge of the wastewater into surface waters is regulated by state permitsunder the National Pollution Discharge Elimination System (NPDES) program (40 CFR 122–125).

Solid waste collected from residential, commercial and institutional sources is separated from other wastes(40 CFR 256–259) and is subject to treatment, storage, and volume reduction (40 CFR 264), or materials recovery(40 CFR 245). Solid waste classified as hazardous material are identified, transported, and processed under morestringent criteria (40 CFR 260–280).

Control over these various forms of municipal wastes has been instrumental in improving the quality ofeffluent discharged from municipal wastewater treatment systems and in meeting the performance criteriaestablished by NPDES. These various controls also create conditions that can improve the quality of sewagesludge, and increase the likelihood of meeting the standards required by the Part 503 Sludge Rule. If it were notfor this regulatory framework and investment by industry, beneficial use of sludge would not be a viable option.

If the quality of sludge does not meet beneficial use criteria, it must be disposed as required under the Part503 Sludge Rule or, if mixed with non-hazardous solid waste, managed under existing state solid waste plans (40CFR 256 and 258). Sewage sludge is now regulated under the solid waste rules only if it is mixed with municipalsolid waste and disposed of by means not covered under the Part 503 Sludge Rule, which otherwise covers all landapplication of sewage sludge. In this regard, the credibility of sludge beneficial use programs may be improved ifEPA and states assign authority to local government solid waste regulators for


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FIGURE 8.1 Some of the processes in the wastewater and sludge life cycle generally addressed by federal and stateenvironmental regulations.

responding to any reports of inappropriate activities related to beneficial reuse of sludge, such as excessiveapplication, odor, or illegal dumping. Some of the negative public reaction to land application of sludge may bedue to an erroneous public belief that prohibited materials may now be land applied.

Treated Effluent and Sludge Discharge Management Options

In the regulatory framework diagram illustrated by figure 8.1, treated municipal wastewater effluent can bemanaged through two options: disposal to a surface water discharge point assigned by the NPDES permit (40 CFR122–125), or by meeting state standards for land treatment, land disposal, or wastewater reuse. Usually, additionalpathogen attenuation and/or crop selection and harvest restrictions are imposed if the effluent will be applied tocrops intended for human consumption.

Treated sewage sludge can be managed for either disposal or beneficial use. Sludge can be disposed underestablished solid waste programs (40 CFR 240–299) if disposed into solid waste disposal facilities controlled bythese programs, or it can be disposed or beneficially used under the requirements of the Part 503 Sludge Rule(EPA, 1993). As described in Chapter 3, the sludge may be applied to agricultural land for beneficial use if thetrace element pollutant concentrations are low enough and if pathogen and vector attraction reduction methods areemployed.

Surface and Ground Water Protection

Figure 8.2 shows the processes in food production and solid waste management generally addressed byfederal and state regulations and by guidelines related to surface and ground water protection, especially thoseused for drinking water. Many programs have been established to mitigate adverse impacts from nonpointsources. The U.S. Department of Agriculture (USDA) through the Natural Resource Conservation Service(NRCS), provides technical assistance and controls to mitigate adverse environmental impact related toagriculture. Most of these programs are established through the NRCS (7 CFR 600–611) and they supportactivities such as environmental


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FIGURE 8.2 The processes in food production and solid waste management generally addressed by federal and stateregulations and guidelines related to surface and ground water protection.

services, conservation, and watershed protection (7 CFR 650–658). Many of these programs are specificallydesigned to minimize erosion and contaminant runoff from agricultural land (7 CFR 799, 7 CFR 3100, 7 CFR3407). Erosion control programs can minimize the amount of soil loss (along with any surface-applied sludge) thatmay occur from land application sites.

Crop selection and nutrient application advice by state and local extension agents help farmers to minimizeground water contamination from nitrate leaching. As discussed in Chapters 4 and 6, unsaturated soil is capable ofattenuating many contaminants in sludge and wastewater if they are applied according to crop requirements. Thecontaminants in sewage sludge tend to be immobile and not available for leaching to ground waters. In thiscontext, the use of wastewater and sludge is no different than other agronomic inputs that should be considered inwatershed management and in the protection of ground water resources. When drinking water is drawn fromsurface or ground waters, it is subjected to maximum contaminant and treatment performance criteria under theNational Primary and Secondary Drinking Water Standards (40 CFR 141–143). If public drinking water does notmeet mandatory requirements, suppliers must provide notice to customers (40 CFR 135).

Public Health Protection for Harvested Crops

When EPA first promulgated criteria for land application of sewage sludge to cropland in 1979, some foodprocessors raised a series of questions about the perceived safety and legality of food crops grown on sludge-amended soils, and the adequacy of procedures to properly manage the application of sewage sludge to land usedto grow fruits and vegetables. The principal federal agencies involved—EPA, the FDA, and the USDA—developed a joint statement of federal policy and guidance on the use of sewage sludge in the production of fruitsand vegetables in 1981 (EPA, 1981) to provide assurances to the food industry that the high quality of food wouldnot be compromised by the use of treated municipal sludges with adherence to proper management practices.However, the food processors were not convinced (National Food Processors Association, 1993) as earlierdiscussed.

Neither USDA nor FDA have specific regulations for the use of sludge or reclaimed


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water in food crop production, but rely on existing regulatory programs involved with the consumption of animalproducts and foods that are commercially processed or receive cooking in commercial establishments (illustratedby Figure 8.3). Food processors and retailers normally operate under the assumption that all raw meat haspathogens and handle it accordingly. The principal regulatory protection for meat that is cooked at home is theUSDA meat inspection program (9 CFR 301–391). The USDA requires mandatory inspection for all meats andmeat products under 9 CFR 301–335, and has the enforcement capability to act on criminal offenses. However,since meat is a perishable commodity, improper preparation or handling of meat can encourage the growth ofpathogens and toxic substance even after inspection. Therefore, consumers need to be educated as to the hazardsinvolved in meat preparation and cook meat thoroughly. The food industry and health regulators educate the publicto raise awareness of the food-borne illness risk associated with any improper food handling practices. Noregulatory program can be expected to eliminate this risk, and vigilant cooking practices are necessary for healthprotection regardless of whether a beneficial sludge or wastewater program is in effect.

Standards for inspection and certification of fresh fruits, vegetables and other processed food products areprovided under 7 CFR 51–75. Standards related to the condition of containers and their inspection are establishedunder 7 CFR 42. FDA is directly involved with regulatory controls over food processing practices for harvestedfoods under 21 CFR 100–199. These regulations address issues of specific food labeling, standards for quality,unavoidable contaminants in food for human consumption (21 CFR 109) and help assure that ''GoodManufacturing Practices" are applied during manufacturing, packing or holding human food (21 CFR 110). TheGood Manufacturing Practices (21 CFR 110) are an extremely effective self-regulatory control mechanism wherespecific regulations do not exist. They require the use of only wholesome, unadulterated products and the besthandling methods possible. If a consumer of a processed food becomes ill and the episode is traced to a problemduring food processing, the company will be measured against this standard as part of the basis for assigningliability. Enforcement policies and methods for dealing with criminal violations are covered by 21 CFR 7. Theseregulations guide production processes and use of additives, and establish lists of direct and indirect foodsubstances that can be considered safe additives (21 CFR 184–186). Substances prohibited from use in humanfood, or prohibited from indirect addition to human food through food contact surfaces, are also evaluated andlisted (21 CFR 186–189).

FDA, acting under the authority of the Public Health Service Act (42 U.S.C. 243 and 311) and the EconomyAct (31 U.S.C. 686), developed a Model Food Code. Each edition of the code incorporates the latest and bestscientifically based advice available for preventing foodborne illness. The Model Food Code has been adopted bylocal, state, territorial, tribal, and federal agencies who are responsible for inspecting and enforcing federal, state,and local laws related to safe food handling practices at the retail level. Assistance in implementing the code isprovided by the FDA under the Federal Food, Drug and Cosmetic Act (21 U.S.C. 301). This may be the mostimportant protective activity that exists within the regulatory framework because it promotes uniformimplementation of national regulatory policy for food at retail establishments throughout the United States.

Uncooked food sold by retail establishments and food consumed at home by the public is not directlyprotected by the Model Food Code. Vegetables that may be consumed uncooked need to be properly handled,regardless of whether or not beneficial reuse practices are implemented.


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FIGURE 8.3 Some of the Processes in Food Crop Harvest and Food Production that are Addressed by Federal andState Regulations and Guidelines.

In general, fresh produce requires a higher level of protection from pathogenic contamination during harvest,transport and storage than do crops destined for commercial processing. The Part 503 Sludge Rule requiresfarmers who grow produce crops to adhere to rigid cropping and harvesting practices if Class B municipal sludgeis land applied. The federal regulations require a statement by farmers that they have complied with therestrictions on cropping and harvest. However, no training or certification is required for farm workers, nor is anycompliance inspection or surveillance included in this program.

Protecting food during transport is another critical aspect of food safety. Food products that are intended fordirect human consumption or for indirect consumption, such as feed for grazing animals, may be contaminatedfrom a variety of sources during transport for distribution. If harvested crops were "backloaded" in vessels used totransport Class B sludge,


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crops could be exposed to pathogens. Congress has provided agencies with the authority to deal with this problemby enacting the Sanitary Food Transportation Act of 1990 (Public Law 101–500). Section 4 of this act requires (1)appropriate recordkeeping, identification, marking and certification or other means to ensure compliance. (2)appropriate decontamination. Section 5 prohibits transportation of food products in cargo tanks, rail cars and tanktrucks that are used to transport nonfood products that would make food unsafe to the health of humans oranimals. The existence of the this law, properly enforced, should act as a deterrent that would minimize thepotential of backhauling harvested food products in vehicles that were previously used to transport sewage sludgeto agricultural areas.

Analysis for Regulatory Gaps and Overlap

An evaluation of the framework reveals that many existing regulatory controls are available to protect theenvironment and public health. Federal regulations governing drinking water are generally considered to becredible. Harvested crops that are cooked and handled by retail operations are also subjected to numerous, specificregulatory controls that have achieved public credibility and trust due to surveillance and enforcement.Agricultural crops irrigated with treated municipal effluents may be even better protected than those irrigated withlocal surface waters due to stringent regulatory standards imposed by state authorities on the quality and reliabilityof effluents.

Industrial pretreatment and source control programs have been effective in minimizing trace elementcontamination of municipal wastewater. These programs have been effective because of a combination of industryself-monitoring efforts, surveillance and enforcement activity by government regulators, and lawsuits by citizenaction groups. The Part 503 Sludge Rule has been adopted as a result of the credibility achieved by the controlover trace element contaminants in wastewater entering municipal treatment works.

Applying sludge that is not pathogen-free raises the possibility of foodborne illness. Food quality is regulatedby a host of specific standards imposed on retail operations (food processors, distributors, and restaurants) by theFDA and state health agencies charged with the responsibility for inspecting and enforcing public healthregulations. These stringently enforced, costly controls have been responsible for achieving extremely highexpectations of food quality by the American public. Even in cases where specific operation standards do notexist, processors and retailers are still constrained by "Good Manufacturing Practices" that require all possibleeffort to protect health. If they are charged by a civil or criminal suit, they must be able to prove that "GoodManufacturing Practices" were employed. Failure to do so can be costly for an industry.

The standards assigned to the use of Class B sludge emphasize site restrictions and farm managementpractices, as opposed to the treatment or microbial quality criteria that defines Class A sludge. Questions havebeen raised over whether Class B sludge management practices present a credible program for monitoring andenforcement. If the POTW is not actively involved with management aspects, then reliance is placed oncontractors and farmers to comply with the necessary site and harvesting restrictions. This is not of immediateconcern for crops that undergo processing operations because of the existing food processing safety standardsimposed and enforced by FDA. Also, retail establishments are obliged to follow proper cooking procedures


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according to the "Food Code." However, neither of these regulatory controls will protect the health of those whoconsume uncooked vegetable crops in retail establishments (e.g. salad at a restaurant) or prepared at home. Ifmanagement standards for Class B sludge are not followed for fresh produce crops that can be eaten raw, publichealth could be compromised.

Public confidence in the use of Class B sludge could be improved by more explicit involvement of local orstate public health authorities. In matters of infectious disease control, public health agencies can quickly step inwith immediate consequences for non-compliance, which can include public notice, fines, immediate cessation ofoperation, and/or product recall as necessary. In contrast, environmental authorities typically impose fines and mayallow offending conduct to continue. Additionally, food safety programs normally require personnel training andcertification. If municipal treatment systems wish to introduce a product of value to the agricultural and foodcommunity, that product must not be perceived as a risk to consumers. The only means to ensure this is to (1)demonstrate that the applied material is safe to handle and meets high-quality pollutant and pathogen limits so thatminimal oversight is necessary after land application, or (2) assure that all personnel associated with transport,application and use of sludge are trained and certified, and maintain accessible records to reassure interestedparties that pathogens and chemical pollutants are being managed effectively.

SUMMARY

Economic incentives play an important role in decisions to pursue beneficial land application of reclaimedwastewater and treated sludge. In many cases there are clear economic incentives for society as well as POTWs topursue beneficial use options, even though revenues from these projects will often be small or nonexistent. Withthe exception of water-short areas, there are only limited incentives for farmers to apply reclaimed wastewater andsludge, due to the low cost of alternative sources of nutrients and water. Thus, subsidies may be appropriate whereregulatory costs associated with reclaimed wastewater and sludge application exceed beneficial use values.However, subsidy programs should be structured to avoid creation of incentives to apply effluent or sludge at ratesin excess of crop requirements.

There are only negligible economic incentives for food processors to accept products produced withreclaimed wastewater or sludge. Benefits in terms of lower raw food costs are likely to be minimal, whereas therisks from negative public perception could be substantial. Negative public perception of food crops producedusing treated wastewater or sludge could have detrimental impacts on consumer demand and the profit andsurvival of firms.

Despite the existence of extensive regulations, public perceptions of significant risks associated withbeneficial land application persist in some areas. Extensive evidence has shown the importance of public educationand early involvement in the design of beneficial land application for successful implementation of reuseprograms. In addition, a number of private sector forces deter inappropriate behavior by the various partiesinvolved in beneficial reuse programs. These forces include common law liability, market forces, and voluntaryself-regulation (e.g. codes of conduct, worker training and certification, audits).

Sectors of society that are hesitant, or may become hesitant, to endorse the concept of beneficial use ofwastewater and sludge in food crop production—the food industry, farmers,


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product consumers, and adjoining property owners—will need to have evidence of adequate surveillance andenforcement of the existing suite of pollutant criteria, process standards, and management requirements. This isespecially important for use of Class B sludge on produce crops. One way to maximize program credibility is torequire training and certification for members of the agricultural community who use Class B sludge to grow cropsfor human consumption.

From a regulatory perspective it is important to remember that the Part 503 Sludge Rule and state regulationsgoverning the agricultural use of reclaimed wastewater merely augment a wide array of existing institutionalprograms and controls that have responsibly mitigated risks from these practices in the past. Related regulationspertain to toxic waste handling and treatment, surface and groundwater protection, and public health. Theseregulations and their overlapping authority are complex and need to be adequately explained to both the regulatorycommunity and the interested public to avoid confusion and the perception that beneficial use is a disguise for thedumping of wastes. Although some clarification and streamlining of the Part 503 Sludge Rule would bebeneficial, the regulatory framework appears generally adequate to manage risks associated with land applicationof both treated municipal wastewater and treated sewage sludge.

The suite of existing federal regulations, available avenues for additional state and local regulatory actions,and private sector forces appear adequate to allow, with time and education, the development of safe beneficialreuse of reclaimed wastewater and sludge. In fact, there are many such programs already in operation.

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and

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-spe

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attin

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t be

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may

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Appendix

COMMITTEE MEMBER BIOGRAPHICAL INFORMATION

Albert L. Page (Chair) is Professor of Soil Science and Chemistry and Chair of the Department of Soil andEnvironmental Sciences at the University of California at Riverside. Dr. Page received his B.A. in chemistry fromthe University of California at Riverside and his Ph.D. in soil science from the University of California at Davis.his current research interest is on the fate of trace elements when applied to soils in the form of environmentalwastes. Dr. Page was a member of the National Research Council's Committee on Irrigation Induced WaterQuality Problems.

Abateni Ayanaba is Manager of Agricultural Research and Seed Quality Management at Del MonteCorporation. He is responsible for the management of varietal development, plant pathology, soil microbiology,and agricultural research; seed quality programs on crops of interest to Del Monte; and development of biocontrolsfor pea and bean diseases. Dr. Ayanaba is a Soil Microbiologist with more than 20 years of broad-based domesticand international experience, emphasizing biocontrol, microbial ecology and physiology, and plant-microbeinteractions. He earned his B.S. in plant and soil sciences from the University of Massachusetts, and his M.S. andPh.D. in soil microbiology from Cornell University.

Michael S. Baram is Professor and Director of the Center for Law and Technology at Boston UniversitySchool of Law, and Professor of Health Law at Boston University School of Public Health. He is also a partner inBracken and Baram, a Boston law firm specializing in environmental, health, and energy law. Mr. Baram receivedhis B.S. from Tufts University, and his LL.B. from Columbia University Law School. His research interestsinclude corporate risk management (facility accidents, hazardous wastes, product safety, etc.); risk communicationlaw and information policy; biotechnology legal and policy issues; and use of risk assessment and scientificevidence for decision-making in regulatory, judicial, and corporate contexts.

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Gary W. Barrett is Odum Professor of Ecology and Director of the Institute of Ecology at the University ofGeorgia. He received his B.S. in biology from Oakland city College in Indiana, M.S. in biology form MarquetteUniversity, and Ph.D. in zoology from the University of Georgia, Athens. Dr. Barrett's research interests includestress effects (e.g., pesticides, fertilizer, sludge, or fire) on ecosystem dynamics; mammalian population dynamics;applied ecology; agroecosystem ecology; integrated pest management; restoration ecology; and landscapeecology. He is a member of the American Institute of Biological Sciences, Association of Ecosystem ResearchCenters, and the Ecological Society of America, among others.

William G. Boggess is head of the Department of Agricultural and Resources Economics at Oregon StateUniversity, Corvallis. He has a B.S. in agricultural business and a Ph.D. in agricultural economics from Iowa StateUniversity. His research interests include the interactions between agriculture and the environment with emphasison water allocation, water pollution and environmental policy. In addition, he is interested in applied decisiontheory under risk and uncertainty, and stochastic/dynamic simulation and optimization techniques. Dr. Boggesswas elected vice president of the Southern Agricultural Economics Association for 1993, and received thesociety's Distinguished Professional Contribution Award for Research in 1987.

Andrew C. Chang is Professor in the Department of Soil and Environmental Sciences, and Director of theKearney Foundation for Soil Science at the University of California, Riverside, California. He received his Ph.D inAgricultural Engineering from Purdue University. His areas of research include the land application of municipalwastes, environmental chemistry of phosphorus, physics and chemistry of organic pollutants, and methodology ofestablishing land disposal criteria. He has conducted a study for the World Health Organization on HumanHealth-Related Chemical Standards for using Reclaimed Wastewater for Crop Irrigation and Sewage Sludges forFertilizer. He has served on several state and federal committees for risk assessment of municipal sludge disposal.Dr. Chang received the 1991 U.S. Environmental Protection Agency Sludge Beneficial Use Award for research,and the 1991 U.S. Department of Agriculture Superior Service Award for Natural Resource and Environment.

Robert C. Cooper is Vice President of BioVir Laboratories in Benicia, CA. He received his Ph.D and M.S.in microbiology and public health from Michigan State University and a B.S. in public health from the Universityof California at Berkeley. He is Professor Emeritus at the Department of Biomedical and Environmental HealthServices, School of Public Health at the University of California at Berkeley. Dr. Cooper's research interestsinclude environmental health, wastewater reuse, microbiology, and effects of water quality on human health. Dr.Cooper participated in the National Research Council's Committee to Review the USGS National Water QualityAssessment Pilot Program.

Richard I. Dick is the Joseph P. Ripley Professor of Engineering in the Civil Engineering Department atCornell University. He received his B.S. in civil engineering from Iowa State University, M.S. in sanitaryengineering at State University of Iowa, and Ph.D. in environmental engineering at University of Illinois. Dr.Dick's research interests are sludge

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treatment, utilization, and disposal. He is a member of the Association of Environmental Engineering Professors,Water Pollution Control Federation, American Water Works Association, and the International Association onWater Quality, among others. Dr. Dick served on the National Research Council's Committee on a MultimediumApproach to Municipal Sludge Management, and was a member of the National Research Council U.S./U.S.S.R.Task Group on External Utility Systems.

Stephen P. Graef is Director of Technical Services for Western Carolina Regional Sewer Authority where heis responsible for collection, treatment, solids reuse and disposal, laboratory, and industrial waste pretreatment andengineering. He received his B.S. in civil engineering from Valparaiso University, M.S. in environmental healthengineering from the University of Cincinnati, and Ph.D. in environmental systems engineering from ClemsonUniversity. Previously, Dr. Graef was Director of Operation at Milwaukee Metropolitan Sewerage District. He is amember of the Water Environment Federation, American Academy of Environmental Engineers, AmericanSociety of Civil Engineers, and the International Association of Water Pollution Research and Control.

Thomas E. Long is a Wastewater Management Specialist for the Washington State Department of Healthwhere he is responsible for community environmental health programs, and for promulgating on-site sewagetreatment regulations. He is also a liaison with the Department of Ecology, revising best management practice foragricultural application of biosolids. Mr. Long holds a B.A. in environmental science from the University of WestFlorida. He is a member of the Australian Water and Wastewater Association, International Association on WaterPollution Research and Control, and the Water Pollution Control Federation.

Catherine St. Hilaire is Director of Regulatory Affairs at Hershey Foods Corporation. She earned her B.S. inscience education from West Virginia University, and her Ph.D. in microbiology from the College of Medicine,Pennsylvania State University. Her expertise is in the areas of cancer research, toxicological evaluations, healthrisk assessments, and regulatory analysis. Prior to joining Hershey Foods in 1990, Dr. St. Hilaire was a Principalof ENVIRON Corporation where she was involved in a number of projects related to the public health risks ofenvironmental chemicals. She served as a Staff Officer for the National Research Council where she worked on anumber of reports including Risk Assessment in the Federal Government: Managing the Process. Dr. St. Hilaire is amember of the American Association for the Advancement of Science, Society of Toxicology, Society for RiskAnalysis, and the American College of Toxicology.

JoAnn Silverstein is Associate Professor in the Department of Civil, Environmental and ArchitecturalEngineering at the University of Colorado, Boulder. She earned a B.A. in psychology from Stanford Universityand a Ph.D., M.S., and B.S. in civil engineering from the University of California at Davis. Her research interestsinclude the application of biological processes to water, wastewater, and sludge treatment; kinetic and processmodeling of degradation of toxic organic compounds by mixed communities of microorganisms; biologicaloxidation and reduction of nitrogen; and the use of pH and oxidation-reduction potential sensors

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to control biological processes. She is a registered professional engineer in the State of Colorado. She is a memberof the American Society of Civil Engineers, International Association for Water Pollution Research Control,American Water Works Asso-ciation, Water Pollution Control Federation, American Society for Microbiology,Association of Environmental Engineering Professors, and the Society of Women Engineers.

Sarah Clark Stuart is a program officer with the Pew Charitable Trusts in Philadelphia and is a privateenvironmental consultant. She earned her B.A. in botany with an emphasis on plant ecology from Pomona Collegeand her M.F.S. from the Yale School of Forestry and Environmental Studies with an emphasis in soil and waterscience. She was Staff Scientist and Co-Program Head for the Environmental Defense Fund's Eastern WaterProgram where she was involved with research, writing and advocacy on local and national coastal water pollutionissues, including sewage sludge management, wastewater treatment, contaminated sediments, and ocean disposaland dredge material.

Paul E. Waggoner is Distinguished Scientist and former Director of the Connecticut AgriculturalExperiment Station in New Haven. He earned his S.B. from the University of Chicago, and his M.S. and Ph.D.from Iowa State University. Dr. Waggoner's research interests include agriculture, plant pathology, and the effectof the environment on plants, especially plant diseases. He chaired a Council for Agricultural Science andTechnology Task Force on Preparing U.S. Agriculture for Global Climate Change. He has been a member ofseveral National Research Council committees, and chaired a subpanel of the Committee on Policy Implicationsfor Greenhouse Warming. Dr. Waggoner is a member of the National Academy of Sciences, AmericanMeteorology Society, American Society of Agronomy, and American Phytopathological Society.

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